If you gain XP from killing Monsters, you would level up and your health would be higher, so does that mean Sans has more than 1 HP now?
In game, that is how it works, but that’s not the way stats work in my own mind ^^
I, personally, refuse to believe the monsters killed each other to attain the stats they have, at least in the original universe. So, they must have gotten them another way, right? I certainly think so, and most can be explained away by training. HP, though, I correlate with Hope. A monster with a great deal of Hope, like Papyrus or Undyne, has a lot of HP. A monster beset by depression and nihilism, like Sans, has almost no Hope at all, thus his trademark 1 HP in genocide. I believe Sans regained his Hope, over the years, especially through love and marriage, and attained quite a lot of HP.
However… now that there’s so much wrong and so little to be Hopeful about, saying nothing of the damage his soul took when his wife died… his HP is failing. It is very low, so much so that a severe enough attack would dust him on the spot. Not 1, but very, very low indeed.