My current formula is
=IF(D$14>EOMONTH($C15,0)-$C15+1,"NA",
IF(OR(DATE(YEAR($C15),MONTH($C15),D$14)<I_ER_START, DATE(YEAR($C15),MONTH($C15),D$14)>I_ER_END),"NA",
IF(OR(DATE(YEAR($C15),MONTH($C15),D$14)<C_EMP_START, DATE(YEAR($C15),MONTH($C15),D$14)>C_EMP_END),"NE",
IFERROR(...