Goal: if today is greater than last day of month, if true then last result of month, if false: lookup yesterday in range $E$62:$AK$645, column 2.
This is the formula:
=IF(TODAY()>$E$643,F$643,VLOOKUP($BK$1,$E$62:$AK$645,2))
Col E= all dates of the year. $E$643 is the 31st December.
Col F=...