Sumpter Valley Loco #18’s tender was put behind WP&YR #80 (ex-SV #20) in 1941. Tender assigned to Rotary #1 from 1947 to 1950. Reassigned to Loco #190 in 1960, and sold with Loco #190 to the Tweetsie R.R.
Sumpter Valley Loco #50’s tender was put behind WP&YR #81 (ex-SV #19) in 1941. Tender assigned to Rotary #2 from 1947 to 1951. Tender superstructure remounted on Loco #71’s original tender underframe and reassigned to Loco #69 in 1951. Loco #69 and its tender were sold to the Black Hills Central Ry in May 1956. Loco #69 and its tender resold to the Nebraska Midland Ry. in May 1973. Resold back to the WP&YR in October 2001.
The way that you can tell which tender was which, is that one of them had a prominent dent on the Sumpter Valley, as well as in its early days on the WP&YR. I think the dent has now been pounded out.