What i understand you to mean is that if Cathars wrote the basis for what was copied, what they wrote cant be older than the 13th century, by definition. So you are looking to prove that nothing in the vms shows anything later, and this will act somehow toward substantiation that Cathars wrote it .
As i doubt you would accept my offerings of 15th century events depicted in quire 13 and 14 as proof of anything, i will just say that if it was a 15th century copy of Cathar writings, inclusion of 15th century stylisms or depictions of anachronistic events would not disprove its being so, it would just put an updated spin on the contents, just like that painting by Jean Fouquet showing la Tour du Temple that didn't exist in 1210, as nablator pointed out. What it did do is show where the place was/is and what it might mean to contemporary or future eyes, since that is the audience, not the people of the past.
I dont think you have anything to gain from your requested smoking gun, nor the lack of it.
As i doubt you would accept my offerings of 15th century events depicted in quire 13 and 14 as proof of anything, i will just say that if it was a 15th century copy of Cathar writings, inclusion of 15th century stylisms or depictions of anachronistic events would not disprove its being so, it would just put an updated spin on the contents, just like that painting by Jean Fouquet showing la Tour du Temple that didn't exist in 1210, as nablator pointed out. What it did do is show where the place was/is and what it might mean to contemporary or future eyes, since that is the audience, not the people of the past.
I dont think you have anything to gain from your requested smoking gun, nor the lack of it.