Does anyone know what system software version started supporting this feature?

VMMI shows 12a as the first feature set that supported PRI with CLID. Don't remember if it was available pre-common code. Cmdl_Guy, Jim Wooten or MarkK may remember more.

I was going to say 13! It would not have been available pcc!

If I remember, I will check my engineering notes tomorrow but I'm sure RBF is right. 12A had a lot of firsts, like networking which was a seperate software back then (12AN).