Thanks. I think one reason I was pleased is that we could now work out what a Dex of 19 gave us in 1e that an 18 didn't.
Is that memory accurate?
Yes. Deities and Demigods explicitly opened up all abilities to greater than 18 in AD&D (note that the DMG did give a kinda sorta preview with strength and the girdle of giant strength) by providing the 19-25 tables for abilities.
That said, the 19 = ambidextrous (or TWF without penalty) had to be inferred from the rules as I don't recall it being explicitly stated, but was instead within the text of Mooglum and Mouser.