There's a multitude of emulsions available, even after a lot of them have been discontinued. Each one reacts a little differently to light, both in terms of requiring more or less light, but also in terms of reacting in various unique ways to light.
I've been in a bit of a funk since Sunday morning when folks noticed Silverprint's post about HIE (High speed IR) and EIR (Ektachrome IR) being discontinued. At least this time, somebody gave us warning about it. Naturally, it wasn't Kodak. Folks called Kodak. The first to call got positive news that it wasn't discontinued.... but everybody else was told that the last cut is next month.