Box car "shortages" were a common complaint in the STMFC
era. I am sure that a shortline near a major terminus like
Portland OR or Seattle WA could receive a real dog's breakfast
of empty cars from its connecting railroads (UP/SP/GN/NP/MILW/SP&S)
if car supply were tight. All clean 40 foot or 50 foot box cars
look alike to a lumber mill...

Tim O'Connor