You do know that you can have multiple versions of Poser installed and running on a system at the same time, don't you?  The only real constraint would be how fast and how much memory you have on that system.  I have run both Poser 9, 11 and 12 at the same time while working through issues with scenes etc.

Poser 5, 6, 7, 8, Poser Pro 9 (2012), 10 (2014), 11, 12, 13