this is a phrase we used in the 50s -- "catch ya later" means "I'll see you later" -- a common parting shot. In fact, in our crowd it was shortened to just "later."
Was used in either a one-on-one situation or in a crowd... as you were leaving to go somewhere (anywhere), that was the phrase you used as you left the area and was addressed to anyone and everyone.. "catch ya later" -- then you would usually get a "later, man" response.
This is a variant of "catch you on the flip side" and refers to the B side of a vinyl record. It is generally used as a way of saying "I'll talk to you soon" or "I'll catch up with you later".
"Hey I'm heading out bro, but I'll catch ya on the B side"