A barrel is only as strong as it's weakest point.

Pits don't heal.

Continued shooting with deep pits can forge (stretch) the steel much like ring bulge caused by steel shot in old barrels. That is one of the reasons they must be honed out before re-proof.

Catastrophic failures are more likely to occur in the first 12" of a barrel as this is where pressure builds/peaks.

YMMV