Indeed it is. Consider the following:

1. "Experience lets you recognize a mistake when you make it again."
2. "Good judgment comes from experience. Experience comes from poor judgment."

Anyway, back to the OP. Since this is an Italian bb and further assuming only one side of the shell is damaged could the mechanic start the tap from the good side and run it all the way through the shell and out the damaged side? That would assure good threads guided the tap as it cleaned up the damaged ones.