Total of 63 unique numbers for steam / transition era, not sure if you at trying to cut off before the Progress logo but I have seen plenty of them behind steam.
I prefer without the Progress logo. Most of the cars produced use the 1954 version (which was used 1954-1972), so they really are too late for steam. (See
http://findarticles.com/p/articles/mi_qa3943/is_199910/ai_n8864086/) The earlier version started in 1948, so yes, you can have some steam overlap, but then you have to watch your engines real close to make sure they match. I know a bit proto-police of me (which is not my normal style)..
Also, my understanding is almost all of the 3-bay hoppers on the C&O were post WWII. They experimented with them before that so there were a few here and there, but nothing wide spread. I've never seen a good reference though. As such, I've avoided the three bays...
So, if your looking for 2 bay, without the for progress logo, the list gets a lot shorter:
Atlas:
2 bay offset side - 5 numbers Chesapeake & Ohio
Bowser:
2 bay GLa - 3 numbers Chesapeake & Ohio
MTL:
2 bay Expanded Side - 1 number
2 bay Offset Side - 1 number
2 bay Rib side Flat End - 1 number
2 bay Composite Side - 4 numbers
2 bay Offset Side Notched End - 6 numbers (2 - 3 packs)
Of those, I've never been able to figure out how many of the GLa's the C&O had, I saw one reference that they came to the C&O via acquisition, but no proof.
So, I'm pretty much down to one Atlas and MTL for the right twin bays. Maybe I shouldn't be so picky.