So as soon as the Extension Attribute is active and machines are checking in and that information is being pulled, you should be able to just create a Smart Group based on the EA results. When you create your Smart Group and go in to add Criteria, the bottom option should be All Criteria, and if you choose that it will show all possible criteria to create the group and should include the EA you created. From there, it's just a matter of setting an 'is' or 'is like' or 'is not' (whatever you prefer) that looks for the version # you specify.
So, for example:
Microsoft Office Version [is not] 1442
Microsoft Office Version [is not] 1448
etc.
Or
Microsoft Office Version [is] 1236
Or
Microsoft Office Version [like] 12
It just depends on how specific you want the results to be.