Thank you in advance for any help!

Using Excel 365, I've created a PowerPivot-based report that shows sales data over time - actuals, performance against plan, and prior year's actuals for the selected quarter. The user is given a filter to select the fiscal quarter. To get the prior year's data for the same quarter, I take the filter value and manipulate it to point to the prior year:

Filter Value: 2021Q02 (in cell E12)
Prior Year's Quarter: =CUBEMEMBER("ThisWorkbookDataModel","[Fiscal Calendar].[Fiscal Quarter].["&LEFT($E$12,4)-1&RIGHT($E$12,3)&"]")

This works fine as is for a single quarter. The issue becomes getting the right prior year values if the user wants to select multiple quarters.

I have tried using a CUBESET to point to the filter values, and that does create a set of values, but I need a way to manipulate each of them, or otherwise create a valid range for the set_expression for a new CUBESET formula. This is where I'm stuck. I can't seem to properly get to the values. I've tried adding a prior quarter field to the calendar table, but that doesn't work as the linkage to the actuals data is tied to the current quarter value. I need to be able to set the "[Fiscal Calendar].[Fiscal Quarter]" values to be the prior year's quarters.

Any ideas?