The early 850 T5's were definitely badged as "Turbo" not "T5", in the UK at least.
For me T5 was certainly not a marque - it was very clearly linked to the iconic T5 engine developed throughout the life of the 850, P1 S/V70 and P2 S60 and V70. They were all 2.3l high pressure turbo engines based on that same original design, yes there were revisions to increase power, reduce emissions and improve drivability (at the expense of fun, if you ask me
) but you can trace the roots of the engine right back across the range.
It's a bit like saying the Rover V8 was a marque, there were SO many revisions of that engine but I don't think you could ever call it a marque. A Rover V8 is still a Rover V8 - the question is which revision of that engine do you have.
Recently however Volvo started using the T5 badge to denote the high performance varients - e.g. the S40 T5 runs a derivation of the 2.5T LPT engine. For me that's the point where "T5" stopped denoting an engine and became marketing speak.
Cheers,
John