Rich, if I would say that some troops carried flags without any stars it would be also correct.
Gen. Patrick R. Cleburne division – the best one in the West – was the only Confederate division whose regiments were authorized to carry their own unique banners (as a reward for their sterling performance on the battlefields) - Hardee style battleflags (blue flag, bordered in white and bearing a white 'silver moon'). They used them through the entire war.
But if you mean famous red flags with blue St. Andrews cross, then 13 is correct.