Good point . . . and I've found this very useful when determining the heritage of a "repurposed" car.  Attached photo shows what was probably the last surviving Ann Arbor 74000-series boxcar.  It was being used as a storage shed in the city DPW yard in Cadillac Michigan.  The original car number was stenciled on the inside above the door opening.

STMFC trivia:  this car was THE prototype for the Speedwitch resin kit.  Ted Culotta borrowed the drawings that Arnt Gerritsen made from our measurements and photos taken that day.

Craig Wilson