Hi, I understand your confusion. When CSY decided to build boats specifically for their booming charter business, they first contracted the building of the boats out to someone else. But when the owner of Caribbean Sailing Yachts inspected the first boats, he thought the quality was shoddy, and determined that the only way he was going to get a proper boat that he envisioned would be to build it himself. So unless it is actually a CSY 44 built by the CSY corporation (and they can give you the serial number to prove it), I wouldn't go for it. Anything else won't be CSY quality.
My husband thinks it wasn't Gulfstar that was contracted, but some other fairly reputable company at the time. And I don't know about 42 vs 44. (edit) But it may be that the CSY charter company bought a few Gulfstars early on and used them in their charter business. I don't know.
Good luck,
Sherry