what comes to mind is to create a label that says 'refer to main' and then in it's suppression formule (general tab/x-2 button) put something like:
{table.field} = previous{table.field}
the only caveat being, if you change groups and this field doesn't change, it will display message, as it only knows to look at the data....not where that data logically belongs.
HTH
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