According to their dates, QSOs with the Marquesas Islands count either for the DXCC entity of Marquesas Islands, or for the DXCC entity of French Polynesia, as follows:

ADIF Name ADIF DXCC No DXCC status QSO date
French Polynesia 175 Current Before 1998-04-01
Marquesas Islands 509 Current From 1998-04-01

Q: My QSL clearly says "Marquesas Islands" and yet Club Log maps my QSO to French Polynesia. Why is that?

A: Even though your QSL states "Marquesas Islands", QSOs prior to the first of April 1998 count as French Polynesia for DXCC, and hence in Club Log also.  For example, FO8AN was QRV from the Marquesas back in 1962 when it counted as French Polynesia, whereas FO0FR was QRV there in April 1998 and counts as Marquesas Islands.