As there are many versions of the panniers I think you will find both finishes are represented, unless you are trying to model a particular engine is a case of pot luck.
Makes sense - the railways did pretty much everything over time...
Anyway, you can always invoke Rule 1 ("I'll run what I want to run...")
It's a spectacular paint job BTW. Really really nice looking. I've got some N-scale stuff here that looks like it was literally dipped in the paint pot! Your finish looks every bit as good as a top notch ready-to-run loco.