Was there a specific year that PDCP was on parts versus just a pentastar? Or did it phase out by part more then year.

Oil pump covers, intakes, Water pump housing etc?

Curious if those markings can help ID a parts year, when no date code.

Not exactly sure what year but anywhere after 1962?
Desoto was dead in 1961 (in Canada at the latest) and this was around the same time as the Pentastar marketing plan was gradually being phased in shortly after that.
So,they could not use the the last "D" in PDCD since it no longer was in production,so to speak.
Most parts that were still in production carried the PDCD moniker well in the the 70's.
Plus a lot of rebuilt cores and interchangable parts carried the PDCD longer after that as well.
In theory it cannot help with "specific " date codes if the casting date is not stamped on it.
My original 68 383 starter did have t he PDCD stamping on it and correct date code.
You can never say never in this hobby

Hope this helps

I don't think there was a hard cutoff. 1966 Hemi intake.

Interesting tidbit, about 12 years ago we had an aquarium tank for a lizard. It had a drain hole with a 1" plastic plug.

One time cleaning the tank I noticed the plug was marked DPCPD! The tank was bought new about that time.