The first time that 427's were ever installed in Camaros
at the factory for public sales was the 9561 (iron block) and 9560 COPO (aluminum ZL-1) cars in 1969. In '67 and '68 Yenko would order a RPO big block SS as well as 427 crate motor and do the swap at their shop. This was a bit labor intensive and then they had the 396's they'd taken out of the cars they had to do something with. With his connections within Chevrolet they were able to exploit the COPO process, which normally built special color fleet cars for taxi companys and low-production special trucks for utility companies and the like. Saved them a lot of time and effort and they didn't have an extra engine to get rid of. Plus these cars were warrantied by the factory so the dealership didn't have to deal with eating any covered repairs.
So the cars built in '67 and '68 were not COPOs, and the once they got the process going in '69 with the factory, those Yenkos built with the COPO process were Yenko COPOs.
http://www.holisticpage.com/camaro/camaros/copo.htm