Add WP to your list. By 1940 some of their double-sheathed boxcars from series 16001-18500 were renumbered to series 26001-26125 and were assigned to bulk plaster service out of Gerlach, Nevada.
Garth, I thought it was the single-sheathed cars, originally numbered 15001-16000, that were renumbered into the 26000 series and some of them given roof hatches. The 16001-18500 cars were double sheathed, were they not?