how to show current along with previous year data if i selected in year list box?

[balasundaram]

=Sum({<Year = {'$(=Max(Year))'}>} Sales)

i need show while open current year data only

its working separate selections only like

while opening its showing current year data,in list box if i selected previous year its showing previous data..but issue is if i selected both previous and current year in list box..its showing only current year...not showing total two year data..

[MK_QSL]

=SUM({<Year = {'$(=Max(Year))'}>+<Year = {'$(=Min(Year))'}>}Sales)