A lot of what you're trying to do will depend on what your data looks like (and the density of values, and the data types).
Can you upload a packaged workbook?
If you are concerned about proprietary data, check out the video here:
I can tell you this: You can't create marks that are not somehow present in your data. Especially dimensional values.
You COULD create 12 separate calcs, one for each of the prior 12 months based on the value of TODAY(). And then use MeasureNames/MeasureValues to display them. Again, a packaged workbook would help me walk you through that.
I am unable to upload the workbook at present, but as soon as I have the opportunity I will upload. I appreciate your help!