After publication in 2008, additional documentation confirmed in 2015 adds two Soo Line series of Airslide covered hopper to the roster on page 113. The first group had been erroneously reported in RP CYC Volume 20 as GACX 43067-43081 leased cars that Soo Line later purchased. GACX 43067-43081 remained leased to Soo Line for many years.
Add: Soo Line 69200-69214, 15 cars built, build date 6-57, Builder's Order No. 8099, 70 tons. Hand brakes are believed to be Miner. Apex Tri-lok running boards/brake steps, Barber S-2 trucks, style "D" side posts, gravity outlets.
Add: Soo Line 69215-69229, 15 cars built, build date 3-58, Builder's Order No. 8110, other data ditto the above.
Reference: Photograph of Soo Line 69200, built new 6-57, published on page 117 of Soo Line Freight Equipment and Cabooses by Kenneth J. Soroos, published in 2014. The caption in the book referenced the information in RP CYC and should be updated accordingly.
Thanks to Eric Neubauer and Ken Soroos for their help in confirming this information.
Volume 17 is sold out and will not be reprinted.