Roughly yes, it is declining. The Flynn effect was just smart people having kids later which has now normalized and reversed (with smart people having fewer kids).
Isn't it always 100, by definition?
I dont think IQ is based on american adults.
It's based on whatever population you're testing, IIRC.
isn't the point that 100 is roughly the average? or 100 at the year they made the test, anyway.