I didn't know that the revisions got posted.... That's still an older edit that I was working on.
As for 1974..... HankB has an 18.5 that he got new in 1974, it has the small turn tabs on the bowl vents and the all plastic wheels (early version) and black hubcaps.
Heres an 18.5 BBQ K with modern wheels... Said to be from 1975....larger bowl tabs and new style wheels but still a "BAR-B-Q-KETTLE" vent.
Heres my 22.5 same vent styles, but older plastic wheels...if '74 had small bowl tabs...then it is my estimation that this to be a 1975 model BBQK. I'd bet money that George wasn't wasting perfectly good materials (wheels, vents, ash catchers) before making the permanent switch. Hence the two styles of ash catchers on 1979 kettles. Its looking as though either 1975 kettles had two different wheel styles. OR 1974 had two different bowl vent styles...
The mid 70s kettle details can get hairy but I'm working on it. With the inconsistency in wheel styles (metal/rubber, plastic/rubber, early plastic, modern plastic) there certainly had to be some overlap in model years back in the day. Reilly got a 1974 catalog I thought, I would love to have a close look at it.
I hope that helps. I'm still working on it.