Did create formulae similar to the following;
Sum up prior 6 months in 2021 (not including the current month)
=SUMIFS($H$7:$H$186,$G$7:$G$186,"="&$P$11,$B$7:$B$186,"="&$P$10,$L$7:$L$186,">="&DATE(2020,12,1),$L$7:$L$186,"<="&DATE(2021,5,31))
Sum up the same 6 month period in 2020...