Question about an RPO code

[72blu]

Hi everyone, recently purchased a 1977 GMC stepside. As I was looking through the RPO codes I noticed the code “9V1 - colour combination - BLA” Through my own research ive found that this was a COPO option that became available when you ordered the truck as a chevy sport. But obviously this is a GMC so im a little confused. I included a pic of the spid.

Thanks again for the help!!