Ups, some correction to P.S.:
=IFERROR(IF((SEARCH(RIGHT(F$7;3);"JANFEBMARAPRMAYJUNJULAUGSEPOCTNOVDEC")+2)/3>=$C$1;1;0);0)
Where:
F$7 is the formatting sheet column of data cell (F), month id row on the report
$C$1 is the cell, containing the number of the first month with allowed input on the report
IFERROR required to properly validate formula
In your case the month conversion formula will be:
=IFERROR(IF((SEARCH(LEFT(F$7;3);"ENEFEBMARABRMAYJUNJULAGOSEPOCTNOVDIC")+2)/3>=$C$1;1;0);0)
Vadim