Tim O'Connor wrote:

I disagree Tony. A 3 dome car USUALLY has 3 compartments, but a 3 compartment tank car does not
necessarily have 3 domes. And construction of no-dome cars began well before the end of the STMFC era.

Not sure I get your point. If we are interested in what freight cars DO, then the compartments matter, and the domes don’t. If you are just a car-spotter or collector of train models, I guess the number of domes would be the visual marker you would want.

Tony Thompson