Ty,
I've got a can of Brodak's and a can of Randolph's non-taunting. The Randolph's is quite a lot thicker (more like maple syrup) and has quite a lot more solids in it that the Brodak's. I would imagine that they are largely the same material, overall, but clearly have some differences. But I doubt is matters much.
I can say from experience that you are taking a chance if you change thinners in the middle of a finish. Might come out OK, might not. I do know that you narrow the window in which the stuff is likely to work OK. But hey, do what you want. I know guys that use cheap lacquer thinner from Home Depot in Sig. And it sometimes works fine. When it doesn't (and when it doesn't, it tends to really not work) they complain about the paint. Oh well, you pays your money and takes your chances. I just want to weight stuff my direction as much as I can. Using the same thinner all the way up is one less thing to go wrong.