How to undo Font Book changes?

I wanted to add some fonts to my mac, so opened Font Book and selectd "Add" and pointed it to a font collection in a folder. It's now installed all gazillion fonts (I'd hoped I'd be able to look through the folder and pick and choose visually...no such luck).

When I open Font Book, the new fonts aren't there. Yet, when I open Keynote, I can now see an incredibly long list of new and old fonts in the font menu.

I've tried using Finder and Spotlight to see if there's a single Font folder into which all these new fonts and others I'd used before are stored, but they appear to have stayed within the original (collection) folder. I did this as I thought if I could locate the correct folder, i'd simply go into Time Machine and wind the clock back a few hours to restore my original fonts.

So. My question: Is there any other way I can simply restore it to the way it was a few hours before? I don't want to use the "Restore standard fonts" as I've got other fonts that I'd prefer to not have to reload.

Any suggestions? Thanks in advance for any help.