Related: 7 takeaways from GM recall hearing. Sen. Kelly Ayotte told Barra that she thinks the lack of a new parts number "goes beyond unacceptable.

GM spokesman Jim Cain said changing the part number is "standard procedure" for a new factory run, as GM tries to bring in about 1.6 million vehicles globally that have faulty ignition switches.

Regulators, watchdogs and plaintiff attorneys have seized on the fact that GM did not issue a new part number when it altered the ignition switch in 2006 as an indication that someone may have ...

In 2007 GM and Delphi Automotive redesigned the spring in an ignition switch, but the new one kept the same part number. Now GM has a new problem in its hands.