Found an duplicate Harris HC part which ran all the way out to 15.2 volts. Notice again how the frequency was falling off just prior to failure. Again, no real excitement.
Grabbed an old Fairchild TTL part thinking that would certainly actually blow up... It did!
What's real interesting is how the TTL parts frequency fell way off, then it takes such a radical jump, rolls off again, then dies a flaming smoke filled room kinda death.
If you found an HC part that runs to 20 volts as you suggest and is linear, stick with that part.