Q: iTunes 12 playlists lost when creating new library in Windows 10

See also Make a split library portable to make sure you're keeping the libraries separate and self-contained, and Backup your iTunes for Windows library with SyncToy for backup advice.

tt2

The contents of an iTunes library is determined by the iTunes Library.itl database file. If you subscribe to iTunes Match or Apple Music then details about your library are stored by Apple and when you create a new library, if you are signed into your account, you may see your previous content available to stream or download. Without these services you may still see your iTunes purchase history. This can be turned off, or you can sign out of the account. Your sign in status is saved in the user profile, so to main two fully independent libraries you may prefer to manage them using two user profiles. Even then there are complications imposed by the way iTunes "associates" a computer with one account when it is used to access purchases which may block it from being used with another account. See View and remove associated devices in iTunes - Apple Support for details.

I can use the shift-start-iTunes method to choose between a number of libraries on my computer and I always see what I expect to see when each opens. If you're finding content missing after choosing a library then something is going wrong. Does it only affect the one library and not the other? What anti-virus software do you run? Some have been known to interfere with the way iTunes saves the data when it closes.

tt2

iTunes is an application that runs on your computer. It can create and open libraries. Each library is associated with a media folder which is where that library will store new content. The library doesn't mirror the content of the folder. You can add data to the folder and iTunes won't know until you also add those items to the library. Likewise if you remove media iTunes only finds out when it tries to access the files. All of the playlists associated with an iTunes library are stored in the iTunes Library.itl database associated with that library. Although there are occasions where a database may be corrupted this typically occurs during iTunes upgrades and deletes the entire iTunes library, not just the playlists from it.

Perhaps you could take a screenshot of your library with the playlists sidebar visible before and after the playlists are removed from it. Is the same content listed in the library in both cases?

tt2

To go back to your original question, the best way to have two separate iTunes libraries on one PC is to have different Windows user accounts for yourself and your wife.  In this case, you'll have your library here:

• C:\Users\user1\Music\iTunes

and your wife's here:

• C:\Users\user2\Music\iTunes

substituting the appropriate user names for "user1" and "user2".  The only issue here is that iTunes is fundamentally a single-user application so it can only be accessing one user's library at a time - in practical terms, this means either disabling fast user switching in Windows or be disciplined about making sure that you exit iTunes when you stop using it.  There are other approaches possible, in that you can configure iTunes so that two users can share the same library, or that each can have a different library but share some or all of the same media files.  To be honest, although these can be made to work they're both in the "one way to get it right, many ways to get it wrong" category - I would not recommend either approach.

You asked "In iTunes, which is the "main" area--iTunes itself or the iTunes library on my PC?".  There are two things involved here, the iTunes application (a collection of software executables, configuration data, and preference files that iTunes uses when it runs), and the iTunes library (your collection of media files/folders plus the iTunes database that keeps track of all your media - think of it as the "catalog" - as well as the definition of your playlists, your ratings, play counts, etc.).  This is the "main area" (and should be the only area) for storage and organization of your library.

By default, this is all contained within the iTunes folder in your Windows Music library, as described above, and the standard structure of this library (or each library, if you have more than one) looks like this:

Lastly, in the context of iTunes "sync" operations refer to one of the methods by which the content of your library, or a specified subset of it, can be transferred to / maintained on an iPod, iPhone or iDevice.  tt2's response above refers to his user tip on Backup your iTunes for Windows library with SyncToy which describes the use of the Microsoft SyncToy utility to create and maintain a backup of your library files/ folders; "sync" here has a different meaning to that within iTunes in that it refers to the process by which two sets of files/folders (in this case your iTunes library and a replica of that library stored on another device) are synchronized.

Take a look under Edit > Preferences > Advanced. I suspect you had set the media folder pointing to iTunes instead of iTunes Media until recently. BTW are the various .xml files shown ones you have made yourself? Typically this is either called iTunes Music Library.xml or has the same name as the corresponding .itl file that it is generated from.

The user tip Make a split library portable has general advice on manipulating a library into the standard shape. If my assumption above is correct the general approach would be to set the media folder back to iTunes, move the library files up one level, rename the iTunes folder as iTunes Media, then make a new empty iTunes folder at the same level as the library files and the media folder, then move the library files and iTunes Media into it. All the while opening and closing iTunes after each change.

tt2

I suspect that at some point you'd chosen something other than the iTunes Media folder to be the media folder, e.g. the iTunes folder instead. As given in the user tip there is a limited set of manipulations that won't break the library. You cannot simply move the artist folders to where you think they should be in one move. If you can tell me the path to the media folder under Edit > Preferences > Advanced, the location of the active .itl file, and the path to a typical track,  I should be able to give you a step by step guide to putting your library back in the correct shape.

tt2

The active .itl file will be the one with the most recent modified date, and that will updated each time you use iTunes. You have to use the shift-start-iTunes method whenever you want to switch to a different library. iTunes will always open the same library that it did last time unless that file is missing. If the missing file was at the standard path of <User's Music>\iTunes\iTunes Library.itl iTunes will create a new empty library without issuing an error message, otherwise it will ask you to choose or create a library.

Given the information provided it seems that Arthur iTunes is the first folder that holds all of the media belonging to this library so this should be treated as the media folder. However it is also the folder holding the library files which should be held one level higher. Do the following:

1. Close iTunes. Make a security copy of the iTunes Library.itl file in the Previous iTunes Libraries folder inside Arthur iTunes. If that folder doesn't exist make it now.
   
   
2. Open iTunes, use Edit > Preferences > Advanced to set the media folder to Arthur iTunes. Do not consolidate if prompted to do so.
   
   
3. Close iTunes, pause and reopen. Check tracks will still play. Close again. If they won't play stop and ask for help.
   
   
4. Move the following items from Arthur iTunes to the Desktop:
   Album Artwork                    (folder)
   Previous iTunes Libraries     (folder)
   iTunes Library.itl
   iTunes Libary.xml
   iTunes Library Extras.itdb
   iTunes Library Genius.itdb
   sentinel                              (hidden file)
   
   
5. Shift start iTunes and open the iTunes Library.itl file on the Desktop.
   
   
6. Check tracks will still play. If they won't play stop and ask for help.
   
   
7. Close iTunes. Rename Arthur iTunes to iTunes Media. Launch iTunes.
   
   
8. Check under Edit > Preferences > Advanced that the media folder is now ..\Desktop\iTunes Media. If not make the correction manually, then close iTunes and reopen.
   
   
9. Check tracks will still play. If they won't play stop and ask for help.
   
   
10. Create a new folder on the desktop called Arthur iTunes (or whatever you want really). Move the same set of items inside it as given at step 4 and the iTunes Media folder as well.
    
    
11. Shift-start iTunes and select the iTunes Library.itl file inside your new folder on the desktop.
    
    
12. Use File > Library > Organize Library and tick both rearrange and consolidate options.
    

The folder on your desktop is now a portable library. You can move or rename the folder and reconnect to the .itl file inside it without breaking the library. A clone of the folder made using the process given in Backup your iTunes for Windows library with SyncToy will also be a valid working version of the library.

tt2