Thanks for going to the trouble of posting complete data on your sources. Evidently none of the authors mentioned (including Mr. Hartzler) knew of the Texas physician who happened to have nearly the same initials as your Maryland ancestor. It goes to show that even perfectly respectable sources contain errors.

If someone can explain how Dr. Arthur K. Middleton of Texas could not have served with the 2nd Texas State Troops, this discussion should be continued. Without that or a Confederate service file for your ancestor, I have nothing more to offer on the subject. You should contact Dr. Hambrecht and Mr. Hartzler and let them know about the other Dr. Middleton. I'm sure both men would be pleased to correct their data.

You should also thank George Martin for pointing out the error. I certainly missed it.