They first started using the Pachmayr grips "around" 1984/85 on the stainless models.
The first year or so the stainless Pythons shipped with the standard walnut target grip
I doubt a 1980 Python was shipped with Pachmayr grips.
With Colt, it's hard to tell, but I don't think they ever made Pachmayr grips standard on the blued Pythons.
They seemed to use walnut on blued versions right up until they started using the Excalibur-made laminated grips on the Python Elite.
Apparently Colt DID ship later blued Pythons with Pachmayr grips, but I'm not sure that was "standard" or just a temporary thing.