Yes, RT = Rear Tank
San Louis & Santa Maria Valley RR ordered a 2-4-2T (8-14 1/4C #7) in 1875 named "Avila". Then in 1882 purchased an 8 wheel tender for it.
There's a ALCo builders photo on Bruce Pryor's site [
narrowmind.railfan.net] that shows a 2-4-2 saddle tanker with a tender.
Another photo on Bruce's site shows a pair of 0-6-2T with 4 wheel tenders.
I've heard of a few tankers here-an-there that were given tenders when their duties called for longer hauls than originally intended. Though why they would order a tanker with a tender...maybe they would have had rail and/or bridge issues and needed to spread out the weight rather than put the cost of the tender into a bigger engine?
Cheers,
Curtis F.