ALLSELECTED help for use with multiple values

Hi Everyone,

I have a report that has button filters for years. I have a gauge visual grouping with one gauge showing the current year selected and the second gauge showing the previous year to the year selected. Below is the current dax measures for the gauge visuals now. Right now I have single select on, but if the user holds ctrl and selects multiple years, then the visuals show errors. I have been trying to think of a way where 2 years could be selected and the year prior to the Minimum selected would show in the 2nd gauge. I tried different things but haven't found a solutions yet. I wanted to pose the question to everyone here and see what ideas people may have. Any ideas or help would be appreciated.

Year Selected =
VAR StartDate = DATE(ALLSELECTED('Date'[Year]), 1, 1)

VAR EndDate = DATE(ALLSELECTED('Date'[Year]), 12, 31)

VAR Result = CALCULATE(
                 DIVIDE([Transplant Tissue Totals], [Transplant Rate Denominator]),
                 DATESBETWEEN('Date'[Date], StartDate, EndDate)
    )

    Return Result

Previous Year of Selected =
VAR StartDate = DATE(ALLSELECTED('Date'[Year])-1, 1, 1)

VAR EndDate = DATE(ALLSELECTED('Date'[Year])-1, 12, 31)

VAR Result = CALCULATE(
                 DIVIDE([Transplant Tissue Totals], [Transplant Rate Denominator]),
                 DATESBETWEEN('Date'[Date], StartDate, EndDate)
                 )

Return Result