OK, sorry, my mistake. From the statement in the first post of the thread I thought that Early Girl F1 was PL and that you were using a PL version of Black Krim. I see now that you used off-types from both parents with unknown stability and unknown filial generation, but both potato leaf.
The PL trait will be present and fixed in the new F1, as you observed, since it is a recessive trait on both sides of the cross. Best practice would be to treat the F1 the same way as you would an F2 from a cross of stable varieties, and grow out to maturity several plants in order to compare.
A PL Early Girl may indicate a self pollinated seed from the parental mother, if indeed the mother is PL.
A PL Black Krim must be a result of an outcross somewhere down the line. I initially thought you were referring to a stabilised PL version of it, but I was wrong and you found an off type in a population of RL Black Krim plants.
The main point of my previous post remains the same; if one or the other of the parents is not stable then the F1 of the new cross will show segregation.
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