Run TT from 2 different years at same time

I run my TT from CD downloads. I do everything offline. I used to be able to run the years TT I'm working on and also the prior year's TT at the same time on my computer so I could easily click back and forth to see what I entered the prior year. Now, TT won't let me do this without switching users and running TT from prior years with 2 different users.   Why?  I don't want the tax filing documents; I can access those from my Acrobat.  I want to see step by step method from TT itself. This is all offline.