At Candlekeep, you can meet, but not recruit, Imoen ; this Imoen (IMOEN.CRE) is a mage (!) with weird stats (12/10/9/12/12/10).
This is an invisible glitch unless you install TOB-style NPCs from Tutu-Tweaks. Its description is
ToB-Style NPCs
This component will alter all joinable NPCs to join in the same fashion as Throne of Bhaal, where NPCs immediately level-up upon joining, with a caveat: all creature files are moved down to their lowest experience version, so if you pick up an NPC early enough they will not level upon joining. However, later in the game they will, allowing you to select weapon proficiencies, thieving points, and other goodies from the level-up process.
But for Imoen, this component seems to use IMOEN.CRE as the level one character, not IMOEN1.CRE as it should be ; then when you meet Imoen after Gorion's death and you are level 2, Imoen is a mage.
I know you don't maintain Tutu-Tweaks, but maybe Candlekeep Imoen should be really a thief with her real stats ?