Corrected entry: Sam's coat is unbuttoned (with no tobacco pouch string showing) when he enters his office foyer the day after Archer's murder, but in the next shot (when Archer's widow calls to him) it becomes buttoned in order to hide the string to his tobacco pouch, which he unbuttons and reaches for in a later shot when reviewing the case with Effie.
Corrected entry: When "Sam Spade" is shown the revolver that was used to shoot his partner he correctly identified it as being a British made "Webley". However, he also said that it is a "45-automatic they don't make them any more". The revolver is most probably .445 caliber, 45 automatic cartridges would not be compatible. The movie was made in 1941 and I believe the Webley remained in production at least to the end of WW2.