yeah I think they just used what they have sometimes. this truck was built 11/79 making it a 1980 model year.
I had a 87 blazer back in 88-89 I bought 1 year old and it said fuel injected on the rear gate, 5.7 tbi on the option sheet and that mother f-er was carbed from GM and it was a 10/86 truck title and vin window sticker, efi badges and all. I took it back to the dealer and they scratched there heads also but it was a preowned truck so nothing I could do, nothing they could do. I even called the original owner as there reg card was still in the truck. it was a older guy who said he did not do anything at all to the truck it was just too much of a pain in the ass getting the top on and off the back so he traded it for a extended cab truck when they came out in 88