Nothing in the preamble implies that there are unique answers for the clues; as long as you get only one valid set of grid entries, that should be satisfactory.
For example, consider clue 12 down. No matter what, if the prime X is ab and the entry is cde, then any of these would be valid values for the answer to 12 down: abcde, cabde, cdabe, cdeab (unless any of them repeat some other answer) since they all have the same digit sum. There are a couple of other clues where there are two valid answers for the prime-entry pair.