I had never heard of the term "blown out", until I took a used, wooden clarinet that I picked up for $50 to my tech. He is an English horn player. He told me me that it was "blown out", in addition to the obvious stuff I saw wrong with the instrument that needed work. (Pads, as well as a minor crack.)
Since I didn't know what it meant, I asked him to explain it to me. He did explain, and was even able to show me the change in the bore's shape caused by the years of playing, and most likely lack of proper attention. When you compare the wooden clarinet I have to another clarinet, it is easy to see the difference.
Certainly not all wooden clarinets will suffer this fate. (For example, my late 1800's C. Jeuffroy (Noblet) Albert system is A-OK.) It all comes down to how much they are played, and how they are looked after. However, those that get "blown out", can have their intonation and tone affected by changes in to the bore.
Should I ever get around to it, I now have another potential lamp project. It's too bad really. I would have liked to play the mid-century Richard Keilwerth clarinet. It is like the kid sister to my bass.