The 1P Google Doc is a user initiative to log all the battle loot. Generally things like books are for win 5 from an opponent. [Topic=893024] has some loot for opponents, though it's admittedly a bit out of date.

Also when in doubt, you can look up the book on https://www.subetalodge.org/ and it should tell you which challenger it comes from.

You can either search for the specific item on Subetalodge

or

Use this user run google doc that tracks it

Thank you both of you!

loot books drop on the 5th win, and I usually just search them individually at Subetalodge to find out who drops them. This search should show you them all

As a word of warning, some loot books require very high level pets to win. Battling is not cheap, especially at end game.

Follow-up question, this book Isnts in the spreadsheet or it doesn't say on subetalodge.

I don’t remember if that’s actually loot. I’ve always gotten it in the book nook or from other users.

It's probably given out by an opponent as a random loot drop past 10 wins. But you're unlikely to locate the opponent in general. It's certainly not locked to any specific challenger, and you're more likely to just get it from the shops.

I also went through and updated that The Guide to Challenger Loot. That will have all of the challenger locked 5th win drops.