According to the gamarah in Megilah Targum shel torah is from Unkeles and shel naviam is from Yoneshen Ben Uziel. So howcome in the Chumash I have both targum Unkeles AND Targum YBU?
The Gemara could be referring to the main Targum. There was more than one Targum. Reb Yosef also made a Targum. I think I’ve heard of a theory that the other Targum in our Chumash is really Targum Yerushalmi, and was abbreviated to TY, which was mistakenly unabbreviated to Targum Yonason. It’s a hard pill to swallow, but if you like it feel free to swallow it.
There are a number of studies that have concluded that what in many chumashim is called Targum Yonasan, was not written by Yonasan ben Uziel. Rather, it is an unattributed targum written in Eretz Yisrael during the times of the mishnah and its correct name is Targum Yerushalmi. One theory of how this error occurred is that some early manuscripts referred to this Targum as T”Y, which printers erroneously took to mean Targum Yonansan. The gemara makes clear, however that Yonasan ben Uziel wrote on Nevi’im and not on chumash. Regardless of who authored it, the Targum is very authoritative, was written during the time of the mishnah, and the mystery about its name should not detract from its value.