Unlock cells for a particular month

Hi,
After going through some posts in this site, I found that, we can use custom validation for locking a cells when the condition is not met.
I have tried using that, But I am not able to get it correctly.
Can you please help me?

I have attached the sheet for your ref.

What I want is, when I enter a month in A2 (Which will always be the 1st of that month), that particular column should get unlocked/should be able to edit that month's column only.
I have just provided on table here, but what I want is for entire column so that, I can use the same formula for a larger sheet

Help Pls.xlsx

Hi

Use this formula for Custom Valdation.

Formula:

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And your sample sheet..

It is working great... Thanks Fortis