Okay, sure. The more data, the better. It is always possible that a player deviates from their normal play; however, that is still possible with 100+ hands.
Still, I would regard 20+ hands as a reasonable measure of those particular stats. I can be wrong, and I should not consider it as significant as 100+ hands, but depending on the kind of player, it is still reasonably useful to some extent. Especially when you are up against calling stations. If you're unsure about someone, assume them to be TAG, unless the evidence points to the contrary. But someone with stats like 80/10 when I have seen only 19 hands? I am definitely not doubting the stats then. I will try to exploit that villain before anyone else does. Not only is the probability of them having 19 playable hands in a row very low; in addition, the fact that they are limping/calling so much compared to how infrequently they raise, is a reliable tell IMO.