Pegoretti was sub-contracted to build team frames for Pinarello, presumably because of the desire for custom sizes. I have a titanium Pinarello (badged Opera) I would be amazed if that was built by a Pinarello employee in the Treviso factory. I doubt they would have the expertise.
These days, I don't know what comes out of the Treviso factory. All their carbon frames are made in Taiwan by an OEM manufacturer.
The fact that Pinarello have just penned a deal to have Halfords sell them tells you something about how they want the brand name to work for them (not a coincidence that the only British pro tour team use them)
I think in the days of metal frames all sorts of stuff went on. There are rumours of many riders riding Litespeed frames made up to look like other things, including OCLV frames.