Found a wee little bit supporting the idea it meant Forrest himself was on the field. It appears, according to his premier biographer Wyeth, that only the escort used the 12 star flag. Morton's battle flag, for instance, has the 13 stars. Now, if Forrest's escort was the only one to use the 12 star flag, then that might well be the meaning - they were the elites and they always contained the general. Interesting!