Gus L
Adventurer
There are other concepts of balance in even the oldest systems, and many of these have made their way into OSR and Post-OSR design. The major one is "Level Based Balance". What this means here is that dungeon level (originally literally and often exactly) corresponds to PC level. So a level 1 dungeon is largely balanced for 1st level PCs while deeper levels (or simply locations described as "suitable for levels x to x") are designed for higher levels. This is baked into OD&D in the form of the standardized random encounter tables in the original little brown books.OSR may not be "balanced" but there is an expectation that the GM telegraphs danger to the players so they can make informed decisions. If a 5e GM telegraphs a dragon cave, the players may assume that the dragon is level appropriate. If the OSR GM telegraphs a dragon cave, it may be their way of telling players avoid it and come back later when you are level appropriate, though players can also ignore that telegraphing to their own peril. Some OSR GMs will even be pretty open and transparent about things like, "Hey, you can tell that the area of this hex is more dangerous than where you have previously been."
What's interesting is that this Level Based Balance is combined with Asymmetrical Encounters. Individual encounters may be "over leveled" for the expected party (though with the flatter power curve of OD&D and many OSR editions/games this is less of a risk), even if the level as a whole is not. This is because encounters, and especially random ones, serve the purpose of creating risk and threat - because players aren't meant to seek out combat. Combat is usually inevitable (that "inevitable fail state" thing) but the players are expected to delay it and scheme around it as much as possible, picking fights they think they have the best chance at or those that have a greater reward ... because the fight itself will offer little in the way of rewards.
So while the OD&D encounter tables can end up placing a gargoyle (weapon immune and rather dangerous to 1st level PCs) on the first level of the dungeon, the players are expected to recognize the level of danger involved and find another way to deal with the threat - usually by fleeing. In modern Post-OSR play recognizing the danger will be more reliant on referee description and hints, while in groups attempting to emulate older "boardgame" or "classic" styles of play the players are expected to use meta-knowledge of the monster list.