Most part-time contracts end 31st May (as loan deals), as that is when any end of season finals and play offs are supposed to be done by.
Retained lists aren't given at the end of contracts, they are to announce who won't have theirs renewed, so usually come out not long after the final game of the season.
King's Lynn are expecting to either be promoted, or the season nulled fully, and therefore there is little chance they will any games to play this season. There is still the chance we'll have a play off game or 2 to play.