*scratches head*
I have this vague memory of
Gollum telling
Frodo and
Sam, in Book Four aka the second half of Two
Towers, that
Sauron, whom he must then have met face-to-face, only had nine fingers. This would be a case for someone with a text-searchable file version of TT to scour for. At least today I don't have the nerve to do that kind of digging through the wood-pulp text (I gave the index a try, but found nothing pointing to my suspicion).
I just had this other thought: since Sauron apparently had to rebuild his bodily form from scratch in
the Third Age - couldn't he have "repaired" the missing finger??? 🤔