Consolidate files tells iTunes to make fresh copies inside the designated iTunes Media folder of any content that is connected to the library and stored outside of the iTunes Media folder, changing the pointers in the database to refer to the new files. If you have used the default option in iTunes to copy files to the iTunes Media folder when adding to the library it will have no impact. If you've chosen to keep media spread around different locations or hard drives see Make a split library portable.
Possible causes of metadata not changing, or being changed unexpectedly.
Permissions problems
See Repair security permissions for iTunes for Windows.
Multiple tags (Mp3 files only)
The ID3 specification allow files to have multiple tags in different versions and languages, but iTunes only works properly with single tags. When multiple tags are present it can sometimes fail to apply updates to the tag that it reads back (presumably updating one of the others in the file) and it is also possible that iPod & iTunes may have different rules for which tag they give priority to. This could lead to situations in which everything is properly organised in iTunes but then inexplicably falls apart on an iPod. There are 3rd party tag editors that can manipulate multiple tags but I don't have a recommendation offhand. A workaround in iTunes is to use right-click context menu Convert ID3 Tags... > None a few times to remove all existing tags and then Convert ID3 Tags... > v2.3 to build a fresh tag with the information still held in the iTunes database. I've read in the past that iTunes isn't fully compliant with the v2.4 spec. although this may no longer be the case, however support for v2.3 is widespread so I would suggest using v2.3 over v2.4. Any embedded artwork will be removed so this needs to be replaced if wanted.
iTunes Store metadata (Purchases only)
If you notice that changes you've made to purchased tracks revert to the original iTunes Store metadata then...
In iTunes go to Edit > Preferences > Store and turn off
- Show iTunes in the Cloud purchases
- Share details about your library with Apple
On any iOS device go to Settings > Music and turn off
Show All Music
Close and reopen iTunes and/or reset the device and you should see your version of the metadata for each track rather than the original store data. Sometimes your data won't come back until you play the tracks or use a script such as UpdateTagInfo to read the current data in the tags.
Windows Media Player
See Getting iTunes & Windows Media Player to play nicely just in case WMP is fetching metadata automatically.
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