You may want to make a copy of your app before making those suggested changes.
I suggest that you set up the Key field of your months table to be in the format YYYYMM, so for example a text field looking like
201801
201802
201813
You can use Excel to do an upload for say the next 10 years worth of months, so 120 months.
etc
Then on the detail side of the relationship create a formula called [YYYYMM]
It seems that you are linking the record based on the [Date Created]. I suggest having an override field so that you have the ability to force an entry into a different month, say for example, you get behind in the data entry near a month end.
Then the formula for the YYYMM field on hew child side would be something like
var date DateToUse =
IF(not IsNull([Date Override]),[Date Override], ToDate([Date Created]);
var text YYYY = ToText(Year($DateToUse));
var text MM = Right("0" & ToText(Month($DateToUse),2);
$YYYY & $MM
That should make a YYYYMM field and then you can base your relationship to the months table based on that field.
