Ralph,

The muster roll I'm referring to is a transcript of the original muster roll of the 7th Texas (made out by James L. Newsom). On that list it is clearly noted August 28, 1863 as date of enlistment for John Poore. However, being a transcript, it could be an error.
On the other hand, if Poore was in Company K, he could not have enlisted in that company before October 1862. The authority to enlist a tenth company was only given on October 8, 1862, at which time a number of officers went back to Texas to recruit.
It is also possible that he served only briefly in the 7th Texas before transferring to the 13th Mississippi in October 1863.
Still, he could very well have enlisted in 1861, but I doubt that was in the 7th Texas, simply because I have not found any member of Company K with previous service in another company of the regiment. They were all new men.
This probably didn't clear up your confusion either, but it's pretty much what I can add re. Poore.
It might be worthwile to look into his original service record from Co. K in case the transcription I have referred to is inaccurate.

Lars Gjertveit