Any true breeding variety should be homozygous for dominant traits like RL, as I understand. Any seeds from those Brandywines that grow out RL must be crossed, since PL is recessive. Your Rutgers, on the other hand, would not show PL the second year if they were crossed the first year, and the third year only 1/4 would show PL. That cross should be very unlikely, and you should still be able to identify any RL offspring of the Brandywines as hybrids.
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