In the game "Might and Magic II" (not Heroes of Might and Magic), if I raise the levels of my characters, and then later raise their stats, do the benefits of the now-raised stats work retroactively? I mean, if I level up a few times, and then raise my endurance stat, do I get the benefits I would have gotten if I had raised Endurance before leveling?

If the stat is not Endurance, the benefit works retroactively.

If the stat is Endurance, however, the benefit does not work retroactively.

There is, however, someone who will sell you the hit points you should have.

(Note that this also applies if a stat goes down, for example by resurrection, or as the result of stealing a certain treasure.)

In my experience Endurance does not work retroactively.
So you may want to start with as high Endurance as possible and get the Soldier skill, and possibly Hero skill as well.
And....spoiler ahead...












You get more HP from training in higher numbered towns than Middlegate, with the training facility in Atlantium being the most effective.

Unfortunately towns like Atlantium is not very safe for lvl 1 characters, so shopping around for skills and better training facilities is risky.

Actually, the encounter rate in towns is so low that the later towns are actually not that dangerous at low levels, especially on modern computers where reloading if you do get into an encounter and things go badly is really quick.

You can actually reach every service in town without having to fight any battles unless you get really unlucky or go some way you shouldn't.

Also, "towns like Atlantium is" is not correct grammar; I think you mean "are" there.

(Also, I don't consider the thing you labeled a spolier to be a spoiler. I would consider my statement about the treasure that hurts your stats to be a spoiler, but I think that particular event is so unfun and nasty for the unsuspecting player that any harm due to spoiling it is miniscule compared to the harm a player who experiences the events and then saves not realizing what would happen would experience.)