It just occurred to me that I don’t remember seeing much/any discussion of leveling with milestones in B/X or AD&D, or in OSE and such. This is absolutely not an assertion that nobody’s done it, just me noting that I personally either missed it or forgot it.
How many people have done this in their play, and how did it go? I’m keen on it with more recent editions since I never really liked tracking xp and often want to focus on neither slaughter nor pillage. When it comes to earlier editions, I very much dislike weirdly uneven xp requirements and feel like it’d open up fun-for-me possibilities. But I also know how bad I can be at anticipating consequences, especially mechanical ones where tab A is now going to throw up into slot B.
So please enlighten me! Speculation is okay, but experience is what I most hope to hear.
Hmm. I don't think we ever specifically named or formalized it, but there certainly were times where the DM just levelled people up -- either after a success, before a new challenge (if the party was drastically under-levelled for a situation), or we just wanted to play in a new context (be that name level or just 'after the party gets access to
fly/water breathing/plane shift').
As others have mentioned, because of the different XP charts, we'd be much more apt to give milestone XP blocks than straight levels, but that was no means universal. The game communicated as much, with a very mixed perspective on the matter. Yes, each class had a different XP value, and thus handing out levels as atomic blocks is unfair to the classes where exactly one level is maybe worth less, but there are plenty of examples where the game does that. Adventure modules are rated for parties of characters level X-Y, without concern for what those levels are in. undead were capable of draining a character of exactly 1 level, again without differentiation. Back in oD&D, the XP reward for defeating a monster (direct combat xp and treasure-based) was prorated by comparing the monster level the character level. So it has always been a bit of mixed messages. Regardless, I suspect we did do some occasional 'okay, everyone gain a level' and then the party thief complaining vigorously about the fairness and then some response to that (and handling multi-class characters differently each time, if this was AD&D 1 or 2).
Regardless, AD&D 2e certainly opened the discussion about what xp should be rewarding, and I know we hacked/homebrewed many variations on its' rather unimpressive-to-us* xp for non-loot/monster-defeat actions list. However, this was, IMO, codifying what a lot of people had already been doing (and the game had been alluding to at least since the Dragonlance modules). The game is set up to incentivize treasure hunting, and it is a very fun little game when played towards that end. However, plenty of people, right from the beginning, wanted to do other things with it. Once people realized that their different playstyle didn't meld with the reward structure presented, they modified the system to fit their goals.
*I know we noticed right away that it granted like XP per hd of monster defeated for fighters and per spell level cast for casters, which grew arithmetically, while xp to level grew geometrically in the pre-name-level range; which we did not like.
Overall, I don't think it worked significantly different for TSR-era D&D than it does for WotC-era. Certainly if you give levels instead of XP chunks there will be imbalances (although those are part and parcel of the TSR-era experience). Overall, though, just decide as a consensus what behavior, activity, or accomplishments you want to reward and incentivize, and the rest flows through pretty much the same.