You'd have to ask the person who placed the marker. Evidently that person didn't know that the 115th Alabama never existed. Perhaps the same person misread a handwritten number 4 and thought it was 11. The number 5 is correct.

The original post about this man seemed positive about James E. Warren's dates and military command.
http://history-sites.com/cgi-bin/bbs53x/alcwmb3/webbbs_config.pl?read=34010

Records of the 45th Alabama Regiment are limited. An unfiled record in J. E. Warren's name shows leave of absence granted on March 4, 1864. A pension application to the State of Alabama from Geneva County was made on May 13, 1893. When did this man remove to Thomas County GA?