PO wagons tended to be confined to one specific route, so they’re not really flexible.
I’m unaware of any on the NCC. I think the Courtaulds ones were UTA-owned, not PO.
This rules out Jeeps, Moguls or the two Jintys in terms of hauling anything PO.
The BCDR had the Dundrum PO coal wagons. Some of these ended up on the DNGR, but of course by that stage they were no longer owned by the East Downshire company.
In terms of era, to such extent we had PO wagons, you’re really looking at the 1900-20 period mostly. They’re not really a “modern” thing.
They give colour, of course, to a model goods train. But prototypically, until the 1970s, any sort of goods stock which wasn’t grey was a rarity on all lines.