Hi Ken,
As you said those descriptions are a matter of conjecture as there were not even 12 or 13 states in the Confederacy at the time of the Marshall House incident (May 20, 1861). Arkansas, the ninth state, joined the Confederacy on May 18 and the flag was already made if not flying before then so that leaves Virginia, the eight state which joined on May 7. Moreover, it seems most souvenir hunters usually didn't take the time to peel off or cut around each arm of a star but made a square cut around it. Given the remaining material left over in the canton I don't think there could have been more than 7 stars in a circle in my opinion. Given all the evidence I would say the flag was an 8 star flag.
mike