Great post David. One workaround I've used to find the difference in months between 2 time periods (to @Mitch_Max point) is creating a sequential order against the time dimension using the formula below, and then just leveraging that in calculations through out the model. Then once that is in place you can look up the difference between the periods using a simple lookup. This can be replicated at the week, month, quarter, year levels as well.
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