What percentage of cats that have had anesthesia for surgery, wind up having serious difficulty regu

What percentage of cats that have had anesthesia for surgery, wind up having difficulty regulating their body temperature for awhile even after the anesthiesia seems to have worn off???

I've done just a bit of TNR, & have noticed one person who does it regularly, but does not follow the vet's serious instructions to hold each cat for 24 hours & make sure they don't get too cold or hot due to temporary inability to regulate their own body temperature (a lingering side effect of anesthesia). . . .  I'm tempted to tell the clinic vet about it,, because this person gets a regular discount for doing TNR & helping others like me do it, too.  (I borrowed their traps, but wouldn't give them back until the following day, having held the cats for 24 hours, as instructed . . . after the trap owner said I could just release the cats when I got them home, like they do.)

I don't know the percentage, and I always hold the cats 24 hours in a warm environment.  I would suggest asking the vet involved here.  It could be rare and the vet may just be protecting herself from blame in the rare case that happens.