That is unforgivable from any gun maker...how many hands did that pass through at the factory? There was the assembly tech...the test fire person...any number of inspectors...the person who wrapped it up and placed it in the case...and all missed it? Without more evidence it's pretty easy to say it was deliberate sabotage by at least one employee but most likely lazy employees and inspectors.
If it happened to more than one revolver as seems to be the case...it's probably the same people involved and all should be dismissed for cause and the union should not be averse to that...only to make sure those fired were done so by the book. It hurts the entire company and employees. If any revolvers like that were sent to a gun magazine for test and review it could be catastrophic.
For Colt...in the middle of an attempted comeback...this is ridiculous and management should be diligent in weeding out all these problems hurting the new Python's launch.