My initial game was a BC/BECMI/1e mashup using mostly BECMI rules. We definitely got to the Immortal levels, but not by playing by the rules. No cheating (I think, and IIRC), and we didn't consider it Monty Haul, but we clearly didn't understand the rules completely. I seem to recall the jump from 25-36 involved conning a king out of over 1,000,000 gp per character in the party and everyone shooting up 10-11 levels (no limit on levels gained per adventure). Likewise, the characters that had to start over at level 1 and get back to 36 to gain Immortal status got to be effectively ride-alongs (just had to survive, not really contribute) on high-level adventures backup high-level characters were doing (and thus power-level back to near-the-top). That kind of thing. Basically, we got these new Master and Immortal boxed sets, and by golly we were going to find a way to use them. In that game, I think the highest we got in gameplay was just into Immortal status. Some of the PCs went on to intermediate or higher-power status, but only when they became DM-controlled (the 'gawds' of the campaign world,etc.). No one really found the actual Immortal rules particularly playable, and we kinda lost interest.
More legitimately, we continued with a mostly-BECMI game as older teens, and I got a dwarf character to max level (12) and then to attack Rank E (I remember because he broke the million xp mark). That one was mostly RAW/RAI, although even there I bet we botched rules on XP for gold gained as rulers/commanders and the like (and who knows if we did the treasure tables right).
In AD&D, I seem to recall a ranger that got to name level. Also a human fighter that got to 7 or 8 and then switched to wizard and got back up to 6 or more. We didn't aim as high at that point.
That's one of the problems. By the time we learned to play vaguely 'rules as written/intended,' we advanced to vaguely name level and then kinda stopped caring about level that much.