Going by the P&A's, there were at least 4 chrome lids used between 1967 and 1969!
6422184
6421832
6421746
6422356
What the differences are is beyond me. So therefore, there may have been subtle changes in the design like you're seeing.
The lid I posted pictures of above is original to my car, so I can safely say that in 05D, 1968 (4th week of May), on Wednesday May 22nd (when my car was assembled), at the LA plant, on the L78/L89 engines installed in convertibles, this lid was used!! Before or after that, I can't say for sure.
However, while I can't be 100 percent positive, I believe that most original lids I've ever seen have the cone.
Also note that a chrome lid was used from the mid 60's on the Chevelle, Corvette and full size cars, and well into the mid 1970's on the Corvette and a few other GM cars (with even
MORE part numbers), so even though they're listed for Camaro and/or Corvette, not every lid you see on ebay actually came off a first generation Camaro (or Corvette)!!
Ed