I don't know why this hasn't really come to my forebrain before now, but the more I think about it, the more clear it seems to be that Quayle in BG2 is not the same Quayle from BG1.
First off, his personality is completely different. In BG1, he's a smartassed, condescending braggart who still manages to make stupid mistakes (because, as everyone knows, short people aren't good for anything but comic-relief characters), and doesn't care whom he offends. Come BG2, and he's a reserved, polite, compassionate humanitarian, always trying to play it safe and provide a stable home for those under his care. Next, BG2 Quayle makes no mention of ever having previously met Charname, or traveled in the Sword Coast, and neither does Aerie--and her tales describing her captivity and life in the circus seem to indicate having traveled with Quayle for longer than one year, the timespan between BG1 & BG2. And finally, I'm not buying the whole transition from "I'm Chaotic Neutral, so I'll wait by this road & join the first adventuring party that comes along, because I sure do love adventuring" to "Oh, hi, I decided to settle down and own & operate this circus, and preach the gospel of my Gnomish gods to those under my employ."
Apart from the "remove Quayle portrait" component (of the . . . G3 Tweakpack?), is there any mod out there that
a) alters the BG2 and/or BG1 Quayle to smooth out their relative differences,
b) changes either character's name,
c) adds a conversation option to ask BG2 Quayle if you've met before (and get a negative response), or
d) at least acknowledges that Quayle is a rather common name among Gnomes, making having met 2 of them not a remarkable occurance?