Doesn’t mean it officially exists though - it is just made up by GWR for internal purposes. “Computer says no” if you ask the national vehicle register for Class 255 or 257.
I mean, strictly speaking the national register will also say no if you put 43xxx in as a loco number, (or possibly show the withdrawn warships, it’s been a while since I played this game) all the power cars are still registered as coaching stock from their formative days as DEMU sets.
Officially, they are all Class 43s.
Commonly held view, but aside from a few data plates painted/stickered on powercars - almost all sectional appendix instructions, traction manuals, gauging certificates, statements of compatibility, train crew diagrams refer to them as 253/254 still. If they were officially something else, then there’s a lot of official documentation being produced even now that is wrong.
The argument has been done to death for years. Every time it has come up no one has ever been able to produce any kind of contemporary notice or memo detailing the change in classification - only that it happened a long time ago and despite almost all official documentation saying otherwise that they’re loco and coaches - coincidentally this all seems to have happened round about when most other loco hauled services were withdrawn.