Are you sure that the 2018 Form 1099-R showing the earnings has code P, not code 8? Since the distribution of these earnings occurred in 2018 it should have code 8, not code P, because the earnings are taxable in the year the earnings are taken out. Only the $420 should be reported on a code P 2018 Form 1099-R. Having different codes is the reason why these would not have been combined on a single 2018 Form 1099-R.
