Per your signature you know what Application Version and Tools Release you're running
Background: Application Release constitutes the basic objects like application (sales order, purchase order), reports, tables, business functions etc. Tools Release is the underlying technology that will ensure communication between each server / applications / database / application server etc.
Your system version consists of both.
You can see the Tools Release version by clicking on ? and About in any JDE Application.
To view your Application Release do this:
Login to JDE and fast path to GH9011 On the right hand side expand Environment and then double click on 'Release Master'
The first column of the grid (will most likely be E920 in your case) tells your application release.
No you cannot mix and match different application release versions. You cannot partially upgrade. That said its common for many objects to not be touched by an upgrade so there may be no difference between the 9.1 and 9.2 version of a given object.