Jerry,
Overblowing will flat a reed.
I’ve had several go out by accidentally pressing a key when blowing out the spit valve.
Sometimes if I have a reed that is just a hair sharp I can bring it into line by overblowing it. Thus avoiding having to open and file again.
I’m not sure what’s going on there physics wise?
With filing you are removing bits of material.
I suppose overblowing causes the reed to weaken a little structurally at the base?
They always go flat never sharp.
Someone else want to weigh in with a more precise explanation?