You can use a trick int((date-2)/7) to build a week key. This will be continuous cross years and will be correct in values when you have missing values. The left problem would be easy.
libname s excel 'c:\temp\vol.xlsx' access=readonly;
proc print data=s."sheet1$"n;
run;
data temp;
set s."sheet1$"n (rename=(__2_2002=date __7789=return));
week=int((date-2)/7);
run;