From my notes on this regiment:

"The 57th Alabama Infantry Regiment organized near Troy, Alabama, April 13, 1863. Five companies had enrolled for coastal service in “Clanton’s Legion” at Greenville, Alabama, on February 12, 1863. Five more companies joined this battalion after it moved to Troy. The new command was called Amerine’s Regiment or the 54th Alabama Infantry Regiment throughout most of 1863."

This was simply a case of another regiment being given the same numeric designation. References to the regiment as shown on receipts, requisitions and other documents issued by officers of the regiment refer to it as the 54th until late 1863. This happened to several regiments, including the 26th/50th, the 31st/49th and the 55th/61st. This is just another example.

For another source on battle and campaign history of the 57th Alabama, you might check with R. Hugh Simmons, the historian of the 12th Louisiana. As you know, the 12th Louisiana served in Buford's/Scott's Brigade, Scott being colonel of the 12th Louisiana. The name "Simmons" appears on several notes in the message board archives, and should include a link to his website.

Mr. Simmons has an interesting theory that the flag displayed as that of the 12th Louisiana in Confederate Memorial Hall (New Orleans LA) actually belonged to either the 55th or 57th Alabama based on its location on the battlefield at Peachtree Creek, July 20, 1864.

If you believe they might be helpful, I can forward a copy of my notes on field, staff and company captains of this regiment.