I had this exact problem. I noticed a very small indentation in the roof when I approached the drivers side door in a parking lot one day. I looked closer and saw what appeared to be a very small hole in the top, in disbelief I went home to investigate.
I opened the roof about 3/4 of the way and looked behind the fabric flap on the inside and saw that the fabric had been warn away but from the inside out. The inside of the top was black and white interwoven threads, but in this area it was white due to the warn away fabric. I checked on the other side and the same thing was happening but had not warn through the top completely. It seeomed to have 50% of the original thickness. I tried to take pictures of this, but nothing came out clearly so there is nothing worth posting.
I had searched this forum and found the TSB so I made an appointment with the dealer and went with TSB in hand.
They were nice and took the stuff I provided them with, later that day I get a call from the dealership and they say thay could not find the hole I was talking about. So I went down to show them. The support manager started to postulate how it was probably from a bird or some other animal landing/walking on the roof that had a claw that went through and twisted causing the wear on the inside as well. When I showed him the exact wear on the inside of the top in the exact same spot on the other side (passenger) that did not penetrate and have a hole, he was speechless. He went on about this would be considered regular wear and tear and how a cloth roof would not have warn so easily, he could not authorize a replacement and a whole other load of crap.
At this point I knew that the mustang is a great car, but Ford support sucks and the service of Tower Ford of Great Neck sucks even worse. It seemed as if Ford quality was job NONE.
I will keep a much longer story short, but two days later the Mustang was on ebay and I had a much faster well built car in my garage.
If you have this problem, good luck. To me this gave me insight as to what I will be in for should a real serious problem with the car arise. What I was not fully prepared for was the really poor resale value of the Mustang GT, another eye opener. Anyway, at the risk of being flamed I will end my rant, but the short answer is, Yes I have seen that wear as it led to my no longer having my Mustang GT. F*** the Ford dealers, the replacement cost was 4K that I would have to pay for normal "wear and tear".

 

Exterior inspection of the top should tell if there's a problem. Look for a "worn" spot or "scratches" in the material.