Using the regular five-pointed stars on bikes (decals or pantographs) was not extremely uncommon in Italy. Some marques that are well known in the US include Viner, Olmo and Guerciotti. There were others that used them during certain periods (like Chesini, Esposito or Stella Veneta (although you'll find those more often with a "V" inside a star of David), and others).
There were several marques, all clustered around Padova, though, that used stars regularly in all kinds of configurations: Berma, Vetta, De Franceschi, even Biemmezeta (occasionally). Of those, however, I'm only aware of Vetta using three stars in a line, both in decals and engraved on stay caps and fork crowns. This is why I've always suspected these mystery frames came out of their shop.
The only problem with this theory is that all the 3-star engravings on Vettas that I’ve seen so far only appear on frames from about mid to late 80s. Also, the 3 stars on the fork crown appear on frequently on Vetta branded frames, while the 3 stars on the stay caps seem to only appear on their contract builds.
I even contacted Vetta at one point but never heard back from them.
Here are some pics of stars on decals:
Pantographs on fork crowns:
Pantographs on seat stay caps:
So, my money is still on our mystery frames being contract builds by Vetta (and they’d done a lot of contract builds over the years).