Bards were the ultimate dual-classed character. Start as Fighter, go to 4th to 7th level; start over as a thief, go to 5th to 9th level, start over as a bard. And bards got druidic-type spells. Bard table went to 23rd level unlike others that only went to 20th. (Of course druid and monk were exceptions to the 20th level table; druids got 14, 15, and then Hierophant levels (16-23); Monks got 16 then 17 levels.
High Elves had major limits on levels (these are from memory so mistakes are likely; nevertheless, this is close to how it was):
Fighter 4th level
Str 17+ then 5th level
Str 18/01+ then 6th level
Str 18/26+ then 7th level
Str 18/51+ then 8th level
Str 18/91+ then 9th level
Wizard 7th level
Int 16+ then 8th level
Int 17+ then 9th level
Int 18+ then 10th level
Int 19+ then 11th level
Elves could not get 6th level spells. New spell levels were like they are now (1,3,5,7,9) until 6th level spells which were first gained at 12th level, then the progression went (12,14,16,18). Until late 2e there were no 0-level spells (cantrips) and even then you must give up a first level slot to memorize 4 cantrips. Most mages were considered to have lost, sold, or otherwise got rid of their book of cantrips after their initial training period as an apprentice.
There were other types of elves (drow, grey, sylvan. wild, sea, valley) and each had its own level limits.
Once you reached your maximum level you still split your xp between the two classes, so if one class maxed out early, the other one still moved up slowly. You only had one xp number unless one class had an xp bonus from high attributes and the other one didn't. The one xp number was read separately for each class. e.g 2,000 xp is 2nd fighter and still 1st wizard.
HP were rolled for each class and Constitution bonus was added for each, [but fighters got better Con bonuses than other classes (non-fighter classes maxed out at +2 hp/HD)] then that number was divided in half. e.g. Con 18, fighter d10+4/2 plus wizard d4+2/2= hp/level.
Ciao
Dave