Frequently, we are asked why a QSO with a certain prefix (such as FJ) does not map to a particular DXCC, despite the country or island name being stated very clearly on the QSL card.
The reason is usually due to changes in DXCC status over time. For example, FJ was the prefix for the DXCC country "Saint Martin" until December 2007 when the DXCC rules changed and it became "Saint Barthelemy". The actual island of Saint Barthelemy has always been so named, but its DXCC status has changed.
Club Log is programmed with a very detailed map of all DXCC changes since 1945, so you may wish to experiment with the date controls on the callsign tester. It also includes details of lots of anomalous calls mostly used by ancient DXpeditions to obscure places.