After Mr. Shimoda dies (1:23:29), thieves open his buried coffin and steal his body. This wouldn't have been possible since Mr.Shimoda, like most Japanese Buddhists, would have been cremated the day after the wake. After the cremation, his mourners would have picked his bones out of the ashes with chopsticks, and the ashes would have been transferred to a large funeral urn.
The "locals" speak Tagalog (a Philippine language), not Chamorro, the language of Guam.
The film has the invasion of Guam happening the same day as the bombing of Pearl Harbor. In fact, it occurred three days later, on December 10, 1941.
Many Japanese characters are portrayed by obvious ethnic Filipinos.
Tweed tells Joe he is 32 years old. The real George Tweed was born on July 2, 1902, so was in his early 40s at the time.