Rolling 12 Months formula based on an array of Forward data

Hi Everyone, you've helped me before, but I need further help. I am trying to calculate 12 month rolling total based on selection of month. Can you help me formulate totals in Column Q based off of the month I've selected? The summation is there, I need it to calculate the totals backwards. Similar to before, but backwards. For example, we are in current month December 2019 data, i need summation going backwards to January 2018 (e.g. rolling 12 months to include current December month data) Per the attachment in yellow.

In your Q5 Cell:

Formula:

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Same formula that you have used before... Only the range needs to be modified... That's it.

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