Out of context. Guam was NOT occupied by the Japanese till they invaded it in 1941. Saipan was occupied by the Japanese prior to WWII.
Before WWII Japan occupied Saipan. During WWII the United States invaded and occupied Saipan, and we still occupy it. Before WWII the United States occupied Guam and the Japanese evicted us. We took back Guam during WWII and we still occupy it. That’s all the “hair splitting” context that matters.