If it was the exROD tenders from the Robson 2-8-0s that would be the L.N.W.R. not the L.M.S. If this is the class of tender some of them would be used to up grade some loco classes not forgetting that the L.N.W.R. did also buy some Robson 2-8-0s from the ROD as well, and some would have been used in weedkiller trains, and also for spares.
If it was post WW2 it would most probleby be to provide spares for what I don't know as I've never seen a photo of an ex L.M.S. loco with a ex W.D. Tender.