=COUNTIFS(INDIRECT("'"&A2&"'!A2:A100"),$L$16, INDIRECT("'"&A2&"'!A2:A100"),$M$16)
Column H - I
Jan <=31/01/2020 00:00:00 >31/12/2019 00:00:00
Column J - K
Feb <=29/02/2020 00:00:00 >31/01/2020 00:00:00
Column L - M
March <=31/03/2020 00:00:00 >29/02/2020 00:00:00