My experiences with AD&D, even the one convention/competition I went to where you all played the same campaign in a process of elimination to see who could finish it, is that if your character got above level 10, you were on your way to god status. I always remember playing the lower levels, never the higher ones like in BG2 ... funny I was just doing some internet searching and in the 1st edition AD&D rules had class level limits on whether you were playing a dwarf, elf, etc and some classes were off limits to dwarves, elves, etc. Some class level limits were like 11 and 9 depending on your heritage - and makes me think that the original AD&D rules never intended characters to get much higher than that ... but just a thought - blame the CRPG games for creating level bloat!!!
we never had a legit character get to bg2 kinda levels in pnp, and we had started playing in the late 70s. that said, from the 1980 ad&d rogue's gallery supplement, numerous characters actual played by original d&d developers were included in the final pages. particular noteworthy were the following:
bigby (gary gygax)-- level 13 mage
erac's cousin (ernie gygax character)-- level 7/14 dual-class mage/fighter
mordenkainen (gary)-- level 16 mage
tenser (ernie)-- level 14 mage
robilar (rob kuntz)-- level 15 fighter
robilar, btw, would eventual reach level 19 'ccording a q&a from an old oerth journal. would solo all thirteen levels o' the original castle greyhawk. am not certain what levels gary's characters would eventual reach, but am betting he had at least mordenkainen keep pace with robilar.
so while bioware were kinda making up high level gameplay for bg2 based on what they assumed were s'posed to happen at such levels, the original d&d munchkins did manage to reach such rarified levels. bloat were there before the biowarians and other crpg developers got ahold o' the rules. 'course is anybody's guess what a session involving gygax dming kuntz's robilar through castle greyhawk were like. well, you could ask rob kuntz as he is alive as far as we know, but am not recalling biowarians claim they did so.
HA! Good Fun!
ps erol otus (d&d artist for the rogue's gallery and other works) included his own character. were a ng, high dex fighter. level 12. had a number o' unique magic items.
david cook and jeff r. leason had their characters die and were reincarnated as 'posed to resurrected. ended up with centaur and lizardman characters respectively.
lawrence schick played an elven multiclass fighter/mage (7/11) who exceeded typical level limits based on his 16 str by means o' wish spells.