When Callahan is in the March's apartment with Mrs. March, she claims he left her when they were in Shanghai. Earlier, the split supposedly occurred in Singapore when Callahan shipped out for the war. Shanghai seems even less likely than Singapore as Shanghai was occupied by the Japanese in 1937, nearly 4 years before Singapore fell.
When Callahan is in Frennessey March's dressing room, he states he shipped out of Singapore during the war. The Japanese captured Singapore and occupied the city from February 15, 1942 to August 15, 1945. The three ships sent to defend Singapore were either sunk or ran aground. Callahan could not have embarked on an Allied ship as Singapore was thousands of miles behind enemy lines at the time.
When Callahan jumps through his window to escape from Bone, he leaps, upper body first, shielding his face with his arms. He would not have been able to land on his feet, as shown.
As Callahan is getting up after being attacked by two thugs on Peking Lane, you can see the silhouette of a crew member briefly on Callahan's trousers.