I just pulled out my Weber geek flag, so here it goes..I'd say the non raised/engraved WEBER logo with the tall/elongated "b" in WEBER came about in 1975-76 and was used through 1977. Up until ealier this year, I thought that the raised logo didn't appear until 1979, but I have accquired a 22.5 Copper Mist/Brown kettle that has the raised logo, but no letter/date code. There's pics of the vent in the date code thread. So the raised logo vents sans date code must have come out in very late/Christmastime '77 or just for 1978. As evident from seeing kettles known to be from or puchased new in 1977 to have the engraved logo. As time goes on, we're gathering more knowledge on how to determine the age of a kettle from 1968-78, at least narrowing them down to a window of years from first 1968-1970 PATENT PENDING's (thought to be 1970 only previously)to the 1971-1974-75 pantent numbered B-B-BQ-K's to the 1975-76-77 engraved logo kettles, to the 1978-1979 RAISED logo vent kettles (Previously thought to not exist until 1979 and later) There's also visual evidence that when Weber first updated the lid vent in the mid 1970s to the engraved logo they left the turn tab small and rounded like the old BBQK's however, they retooled the bowl vents from the single rounded mini turn tab to the wide dual tabs that are still made today for the WSM and as replacement vent parts. This is also when Weber would have retooled the wheels to the modern OTS/OTG style whitewalls. 2-3 years later (when changed to raised vent logo), Weber must have thought the lid vent should have the same style wide turn tab as to match the bowl vents. I'd love to put together a section on here explaining what we know about this decade and the others before and since of the Weber kettle. Given everyones collections, we can get visuals from each period to illustrate our points.
Craig