Well, if this report is true about the months of the campaign, there aren't any records missing at all, are there?
Regardless, even if there were records specific to this time, if he didn't get in trouble, or wasn't missing, they would normally have been disposed of soon after he left to go back to Texas. In the Regular military, when one is temporarily assigned to other units, it is all too common for the records not to follow you back to your unit. I myself had to make special requests or in two cases return myself to get records for while I was in training, as they never made it back to my unit on their own. One set of those records had to be reconstructed, as the originals were not to be found (Don't know if they destroyed them, or never transfered instructor records into permanent records).