Jim

Assuming for data, dates (Jan 1 etc) as text in column A beginning at
row 3, and years in row 2 beginning at column B. For table, Jan, Feb
etc in column G beginning row 3, years in row 2 begining column H, use
the following. Expand/move to fit data as necessary.

=MAX((LEFT($A$3:$A$368,3)=$G3)*($B$2:$E$2=I$2)*$B$ 3:$E$368)

Enter as an array (CTRL+SHIFT+ENTER) and copy to remainder of table.

Regards

Murray