I tried to perform this calculation using an 'and' function instead of multiple 'if' statements, and it does not work. Can anyone explain why it doesn't work?

{=PERCENTILE(
if(
and(
NUMBERVALUE(LEFT($A$1:$A$18,4))<=EndYear,
NUMBERVALUE(LEFT($A$1:$A$18,4))>=BegYear,
NUMBERVALUE(RIGHT($A$1:$A$18,1))<=EndMonth,
NUMBERVALUE(RIGHT($A$1:$A$18,1))>=BegMonth
),
$C$1:$C$18),.5)}