My favorite was the Bard - The bard could be a half-elf or a human. To be a bard you first had to dual class in fighter and Thief, then you could take your third class in Bard ..... but half-elves were not allowed to dual class ..... so they could be Bards, but they could not earn the class prerequisites to be a Bard!
That's not it for bard issues.
1e PH page 117: "BARD ABILITIES A bard must have scores of 15 or better in the following abilities: strength, wisdom, dexterity and charisma. Furthermore, a bard must have at least a 12 score in intelligence and a 10 in constitution."
So if you meet those stats you can be a bard right?
Not quite.
Again page 117 "Bards begin play as fighters, and they must remain exclusively fighters until they have achieved at least the 5th level of experience. Anytime thereafter, and in any event prior to attaining the 8th level, they must change their class to that of thieves. Again, sometime between 5th and 9th level of ability, bards must leave off thieving and begin clerical studies as druids; but at this time they are actually bards and under druidical tutelage."
Page 33: "In order to switch from one class to another, the character must have an ability score of 15 or more in the principal attribute(s) ability of the original class and a 17 or 18 in the principal attribute(s) of the class changed to."
Thieves only have a major attribute of dexterity so the dexterity minimum is actually 17 not 15 to get to bard prerequisite training step 2.
Page 26: "The major ability for a thief is dexterity, and a character must have not less than a 9 to become a thief."
So you in fact might need a 15 strength, 17 dexterity, 10 constitution, 12 intelligence, 15 wisdom, and 15 charisma.
And then depending on how you interpret the beginning clerical studies as a druid versus being an actual bard the principal attributes might be the druid's.
Page 20: "As priests of nature, they must have a minimum wisdom of 12 and a charisma of 15. Both of these major attributes must exceed 15 if a druid is to gain a 10% bonus to earned experience."
This would mean you in fact need a 15 strength, 17 dexterity, 10 constitution, 12 intelligence, 17 wisdom, and 17 charisma.
However if you interpret it as then switching to bard class under druid tutelage and not druid, you would need 17s in the major attributes of the bard class, which are not specified, but you do need 15s in four attributes, and minimums in the two others. Conceivably this could be interpreted to mean you need 17's in every stat, or four stats, or since bards do not have the 10% experience options listed, they have no major attributes, just high minimums and just need the 17 dexterity to get to the thief class intermediary training.
Of course it is possible to interpret it as the bard rules are their own thing so human and half-elves can both take the bard class at first level, which are effectively but not actually fighters at that point, and follow the path of the bard without meeting the stat and race requirements of standard dual classing, in which case the stat requirements are as listed under the bard class and the character must switch over to thieving after 7th level fighter progression without having other options to continue as fighters or to dual class to other classes.