81-87 GMC grille changes. Same year change as Chevy?

[Lq9'ed 80 Sierra]

Strange, my 80 sierra came with an 81 front My truck as the straight line fenders and has the later style interior, can someone shine in if the later made 80' models may have looked like the 81-87? I know GM did that to the 2013 impala, you can get the older body style or the newer body style yet they are both 2013's