Validation Rule date can only be changed to date in the same month BUT not changed if the month has already passed

Question

The validation rule I have right now stops reps from changing the date if the meeting has been completed, indicated by a checkbox.

AND(
Meeting_Conducted__c = TRUE,
ISCHANGED( Meeting_Date__c ))

But I am missing one piece. The rule should allow for reps to updatethe Meeting_Date__c if it is in the SAME MONTH as the original value. Once the month has passed, reps should not be allowed to update that field... Any ideas? I thought it would be:

MONTH(Meeting_Date__c) != MONTH(Meeting_Date__c)

I am trying to add the Month check to the existing rule. When I say it doesn't work, I mean the SFDC doesn't even register that line in the rule.

I've also tried doing something like:

AND(
Meeting_Conducted__c = TRUE,
ISCHANGED( Meeting_Date__c ),
TEXT(MONTH(Meeting_Date__c )) != TEXT(PRIORVALUE(Meeting_Date__c )))

Have also tried:

Meeting_Conducted__c = TRUE
&&
ISCHANGED( Meeting_Date__c )
&&
NOT(
MONTH(Meeting_Date__c) >= MONTH(TODAY())
&&
YEAR(Meeting_Date__c) = YEAR(TODAY()))

Answer 1

Your first attempt did not work because...

MONTH(Meeting_Date__c) != MONTH(Meeting_Date__c)

...will always be FALSE, as it is comparing the current value to itself.

It seems that you discovered that, and so changed it to use PRIORVALUE. You were very close, but you changed more that one "variable" at a time in your experiment: There is no need to change the MONTH TO TEXT in this context, so this will work:

MONTH(PRIORVALUE(Meeting_Date__c)) != MONTH(Meeting_Date__c)

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Also:

• You do not need to add the = TRUE to the logic for the Meeting_Conducted__c checkbox - it is a Boolean, so you can just use Meeting_Conducted__c to check for TRUE and NOT(Meeting_Conducted__c) to check for FALSE.
• If you are explicity checking for a changed MONTH (or DAY or YEAR for that matter), you do not need the ISCHANGED() check any more.

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Validation Rule

AND(
  Meeting_Conducted__c,
  MONTH(PRIORVALUE(Meeting_Date__c)) != MONTH(Meeting_Date__c)
)

Using the above rule, then starting with the following data...

...when I tried to change the MONTH, this happened:

...and when I tried to only change the DAY, it was accepted:

When Meeting_Conducted__c was not checked, I was able to change the MONTH, DAY and YEAR to my heart's content.

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NOTE that you will probably want to add a check for the YEAR, as the Validation Rule I posted does not and the user can change the YEAR with it.