This index is wonderful but like any resource is only as good as the information supplied to it. I know one of my ancestor's grave site is wrong and I would think the family member that supplied the info way back when would have known better. He didn't know his civil war ancestor but he did know his wife who is the one buried in that spot. I had emailed Dan McCaskill http://mscgr.homestead.com/indexB.html about where the info came from and he was able to tell me. He would be willing to fix it, only unfortunately I can't offer tangible proof to the contrary of what the relative had sent in so it is what it is unless a relative still in the area can locate the church records from the early days of the cemetery to prove otherwise. Even if his remains were brought back (not very likely), that cemetery and church didn't exist at the time. Now you might get lucky and Mr. McCaskill has something more tangible than a card supplied by a grandson (as in the case of my family) to tell you where the info on the 9th regiment for your ancestor came from.
This is what makes the research so much fun! If it was all handed to us on a platter that would be no fun at all.