DATE Conversion

Hi All I have an date conversion as to which I used a vlookup, Have tried "Choose" but was not able to get it to Work am thinking about Index and Match. Is there an easier way?

IF(ISBLANK(A3),"",IF(A3="ET Mo","",EOMONTH(VALUE(VLOOKUP(RIGHT(A3,2),$D$2:$G$21,2)&" / 1 / "&IF(VALUE(RIGHT(A3,2))<7,VLOOKUP(IF(LEN(A3)=4,MID(A3,1,2),MID(A3,2,2)),$D$2:$G$21,2,FALSE)-1,VLOOKUP(IF(LEN(A3)=4,MID(A3,1,2),MID(A3,2,2)),$D$2:$G$21,2,FALSE))),0)))

attaching the file the field that I am generatoring is the B column, Fiscal date conversion
Thanks
James