heavily weathered covered hoppers at feedmill

[h2w]

we have a small Cargill feed mill that ships out 1-3 covered hoppers a week. you can pretty much count on some really weathered older 3 bay covered hoppers showing up. these cars look pretty much the end of their life. there's other nearby feed mills that ship the same stuff, and mostly get clean  newer cars is there some reason for this or just coincidence?
thanks
 Mark

[Blazeman]

May be a configuration situation for which those cars are unique or maybe a chicken feed delivery which leaves a residue in cars. Rather than clean each after each trip, shipper may dedicate the cars to that piece of traffic.

[cv_acr]

Are the cars all private/lease (X) marks?

Or privates at one mill, and RR-marked at the other?

Could be no more a pedestrian an answer as what cars the shipper is leasing/renting, or if they have the RR supply the cars.