From memory, which I admit is only about an inch long these days, in Mike Venterino's book on lever rifles, I thought I read that the 25-20 WCF (Marlin chambered first) was a BP round. (?)
I am not near the house this week so can't check until later.
At first glance the 32-20 and the 25-20 seem to be occupying the same space in the need to shoot things. Kinda like the 44WCF and the 38-40. But I think the 25-20 is about right for small game. The 32-20 is really able to handle the next class game up to small deer at closer ranges that the 25 really would be a stretch for. (assuming the 32-20 is loaded right)
I have two lever 25-20's and really enjoy them - so much so, I am starting to rebarrel a project low wall action to 25-20 WCF this winter.