Ron Merrick asked:
"Since we've been talking about the earlier part of the steam era, I've noted references in various places about the assignment of USRA car types and how 'some roads refused to accept them'.
Is there a good reference that discusses the cars that weren't accepted, and the reasons the assigned railroads gave?"
Go back to the James E. Lane's definitive article on these cars, published in Railroad and Locomotive Historical Society's "Railroad History" No. 128. It includes a table of the original allocations and a short narrative explaining why railroads refused to accept cars.