If I may add, for the 1978 model year T/A 6.6 decals were used on Trans Ams with the W72 Performance Package, whereas, the base L78 400's and L80 403 Trans Am had blank shakers, meaning no decals. Factory documntation shows no part number for a 6.6 LITRE decal for the 1978 model year. With that said, mistakes did happen and the T/A 6.6 shaker decals could have been added to either base L78 and/or L80 cars. This however would be a very rare occurrence. Stories about factory line mistakes have a tendency to get blown out of proportion, meaning many more mistakes are perceived to have happen than actually happened. If I may coin a phrase from the movie "Stripes"..."it's the stories they tell"
As far as how the W72 engine was recorded on factory documents and build sheets, I have researched this too.
Pontiac Car Distribution Bulletin 77- F-1, June 25, 1976 introduced a new 400-cid engine called T/A 6.6 and available on Trans Am and Formula at extra cost. The new engine was originally to carry UPC code LS7, but for reasons unknown around August 5, 1976 just before the release, code LS7 was changed to code W72. All of the original Pontiac build bulletins and memos identify the T/A 6.6 engine as W72 or T/A 400 in 1977-78 and L78 or T/A 400 in 1979. The T/A 6.6 engine carried UPC code W72 and identified as T/A 6.6 Litre on the 1977-78 Firebird dealer order forms and was available only on Firebird Trans Am and Formula models, except for the 1977 Can Am. All Pontiac bulletins and memos for the 1979 model year list the T/A 6.6 engine in the dealer order guide under UPC code L78.
All 1977-79 Firebirds produced with the T/A 6.6 engine option list UPC code W72 PERF PACKAGE (NORWOOD, OH) or W72 PERFORM PKG (VAN NUYS, CA) on the factory build sheet.
As far as reverence, between 1977 and 1979, the W72 was.... "King of the Hill"