You may have looked at it, but you didn't pause to understand it. Look, not only did I just quote the 1981 Dragon Sage Advice (you know, the one that was
entirely about Bards) that contradicts what you are saying .... but
I also wrote a longer post that touches on the issue.
But sure, let's look at the rule. Bards don't follow the "character with two classes" rule because ... wait for it ... THEY DON'T. Not once they are past the thief part. The second they become a bard (literally, the second) they are a bard. They immediately follow Bard Table III (armor and weapons permitted). They immediately fight as a fighter of the previous level. They immediately use their thieving abilities as a thief of the previous level. Most importantly, they do not have to follow the "two classes" rule to become a bard, because if they did, they would need ... wait for it ... a minimum score of 17 in ... strength, wisdom, dexterity, charisma, intelligence, AND charisma in order to become a bard.
You follow the "character with two classes" rule to go from fighter to thief. Then you follow the Bard rule. Period. Feel free to read it again. They are not a character with two classes; they are a bard.
(The "character with two classes" rule is one of those weird rules that people misapply more than almost any other one.)