the store cars were still on the system in the 1950's, see picture: SAC 7-56.
They were numbered 8051-8085 from the start and went into MW/scrapped.
Why are boxcars assigned to plaster service not assigned to general service?
Not all of them loaded plaster, only 35 of the 125 cars numbered into 26001-26125 had either 2 or 4 roof hatches, see enclosed copy of my 1950 ORER.
The rest was as built -only renumbered and with AB brakes- these cars stayed into service untill the end of WP in 1983.
See diagram & picture in my previous post and enclosed photo by Bob Larson taken in 1970.