This same sort of question came up several months ago, in connection with several locomotives and a host of cars lettered for fictional railroads and industries which were moved from western Ohio to northern Pennsylvania for use in filming a movie.
The answer seemed to be "interchange service" involves a lot more than just the fact that a car moves from one railroad's tracks to another's. Apparently the cars and locomotives for the movie were moved under contracts which specified particular pieces of equipment, to be moved at particular times. That's different from "interchange service" where one railroad agrees to complete a contract for transportation services written by another, and to return or load the empty cars (as governed by car service rules) when that job is done.
Similarly, the PRR gained access to certain coal mines in Indiana County by handing certain cars off to the B&O. The place where this was done was NOT listed by the ICC as "connection for the interchange of traffic" since the hand-off was not considered interchange. The PRR set out certain cars, instructed the B&O which cars were to go to which mine. After B&O took the cars to their destinations, B&O picked up returned the same cars to the transfer.
This is different from "interchange" for then, PRR would be handing empty cars to B&O only if those cars had been received loaded from B&O and would have no control over what became of those cars once handed to B&O. Whether this sort of thing is "a gentleman's agreement" or "a business contract" could be argued. Whatever it is, it's not "interchange service".