If I was modeling an earlier era....

[Sumpter250]

Was browsing and found what looks to be a good deal, a nice lot of 9 HO scale boxcars. Some have truss rods underneath. Metal wheelsets. If I was modeling the proper era, I'd give these a real close look.

Pretty much the only way the "old" stays around is in museums, which is why the Cindys Harbor was conceived as a "working museum". On occasion some of the older equipment is operated in one of the "museum trains", and is otherwise preserved for public viewing. Subcontracting "small loads", and use of trackage rights, keep the museum operating.
Or,
It's conceivable that old equipment might still exist on a modern railroad, but there's no real way modern equipment should show up on and older era railroad. We haven't perfected time travel..........yet.