or is it a "you get lucky" kind of thing?
Not called DVs, but Stat Experience:
In GSC and RBY, Pokemon had what was known as Stat Experience, which functioned similar to EVs. I believe that every time you beat a Pokemon, you gain Stat Experience based on the defeated Pokemon's base stats; so if you defeated a Mew, your Pokemon would gain 100 Stat Experience in each of its stats since Mew's stats are all base 100 (I'm 99% sure this is how it worked). Using vitamins will also give your Pokemon Stat Experience for a certain stat. And yes, it is true that you can max out all your stats in Gens I and II. You can get enough Stat Experience to do this. All you really have to do to max out your Stat Experience is just battle a lot of Pokemon. It doesn't really matter which Pokemon you fight since every Pokemon contributes Stat Experience to each stat and there's no 510 EV limit to worry about. There's no way to check how much Stat Experience you have, so you'll have to keep track.
