Completing sticker book

I still need at least 2 community challenge special hats (the Citron doghouse and Foot Soldier foam pointing finger). I've done them all, so haven't missed any of those, we just haven't had enough of the challenges give us special items as opposed to legendaries (obviously this recent one was to give people the chance to unlock the twilight chomper).

The update added 8 more stickers to my total.  That's after I earned twilight.  I was previously missing one sticker (banana bunker) but suddenly I was short nine.  All the new stickers are on the plant side, but my sticker book does not have an empty slot anywhere.

To add to the mystery, last night I noticed that the differential had gone down by two, even though I had not gained any stickers.  So now I'm only short banana bunker plus six unknown plant stickers.

Yeah, the moving target is frustrating. So close and yet so far!

Thanks, @BillydieBumse .  I had a sneaking intuition about that.  Unintended oversight, no doubt.

8,628/8628 is what my sticker book says.

I've got the eight mystery stickers figured out.  @BillydieBumse was correct on tying it to twilight chomper.  The eight stickers come one by one as you unlock the character upgrades.  Surely this must have been some unexpected quirk of the latest update.  Either that, or we gain stickers in our book when all characters get their upgrades and just never noticed.