Making an album of photos based on the project they're used in (in Photos for Mac) / 'moving' photos from a project to an album

This isn't a question but a suggestion for a workaround if anyone is wanting to do the same as me and having a problem with it.

Photos keeps your original photos and lets you make albums and projects of them based on (I assume) placeholders of some kind. So this isn't really about 'moving' photos per se but creating a collection of them (an album) based on which ones you selected for another collection (a project).

I created a project (a book) initially from an album of favourites. During editing of the project I removed some images which I decided I didn't really like once I'd played with layouts etc, and added in extra ones that weren't originally in my original source "favourites" album but that I added directly to the project from my camera roll or other albums.

Now that I have my project book with just the selected photos that I decided upon including, I want to take all the photos in it and do other things with them, such as export them for sharing online, but not in the layout that they are in the project, just as individual images. But my project contains over 350 photos and I can't recall which 30 or so from the original source album I deleted from the project and which ones I added in from other albums or from the all-photos roll.

So - I wanted to create an album that only included photos that I'd selected and used in the project. First I tried creating a duplicate project (so I wouldn't mess with my project design, which I still want to keep in addition to the new collection) and clicked "clear placed photos" to remove all the photos from their spots in the duplicated project. But it turns out you can't create a new album from those unplaced (or placed for that matter) photos. You can't click and drag them to a new album, or even create a new smart album and tell it to include all pictures that were used in a particular project. What a pain!

So my workaround was this:

1. Take the source "favourites" album and duplicate the album.

   If you want to keep a copy of the favourites album as is, create a third copy of the album as well - see step 9-1)

2. Go into the duplicated source album and duplicate all the images inside it.
3. Adjust the zoom of the folder so that the images are displayed four across.
4. Click just outside the first duplicate, and hold the click and drag to the bottom of the folder to select the entire second column which should all be duplicates.
5. Drag this selection to your duplicated project
6. Repeat for the fourth column (the second column of duplicates).
7. Go to your duplicated project and clear all the photos from their placements by clicking "clear placed photos"
8. In your unused photos drawer at the bottom you will see all the photos, some will be duplicates and some will be alone.
9. For any photo that is only present as a single copy in the unused photos drawer of the project, go to your original favourites album and check to see if it's in there.
   1. If it is, then it's a photo you decided to delete from the project. Here's where you can either delete it from your favourites album (or from the third copy of the favourites album if you're keeping your original set of favourites in addition to the project set).
   2. If it is not, then it's a photo you added from elsewhere and you can find it and add it.

Super clumsy, but this was the best workaround I could find.

Hope it helps someone else.