Why Queen Mary's survivor count varies

Is there a definite number of survivors from Queen Mary?

Twenty is the best total in this account: eighteen were picked up by the British and two by the Germans, while smaller figures often count only one rescue ship's survivors.

Published figures differ because some sources count the men collected by individual destroyers rather than everyone who survived the sinking. One useful total is eighteen picked up by British forces and two by the Germans. Laurel, Petard, and Tipperary were involved in recovering survivors, which helps explain why ship-specific tallies circulate. The different counts show why a casualty figure needs to be checked before two totals are treated as contradictory.