Your scenario placing Duckworth near Mobile, Montgomery or Atlanta provides a reasonable explanation for the image. Here's another factor which may explain rank. Promotions/commissions almost never came through on the date of rank. If your were promoted 1st Lieutenant, your pay rate continued at your prior rank until your commission arrived. Afterwards the paymaster issued additional pay to make up for the period you served at the lower rank.

Something in Duckworth's service file should indicate when each of his promotions took place. As mentioned above , there are three dates for every commission -- 1) date of appointment or election, 2) date of rank (usually the date of vacancy) and 3) date of acceptance. Date of rank will always be the earliest of the three; date of acceptance will be last.

Oftentimes it will help to know about the status of other company officers. Duckworth was elected to fill a vacancy, so it helps to know when the vacancy occurred and who else might have been promoted.

Date of rank was important to each officer because seniority was based on this date.