I'm going off on a tangent here.  

PTIN has to be renewed annually (with a fee).  For practitioners who didn't renew, I wonder if the e-filing prepared under the expired PTIN would fail or at least be flagged.

The number that a practitioner should verify is the PFIN number.  Last March, a friend called me in panic.  Turned out her PFIN was a "made up number" by herself way back when e-filing started, and finally last year her software asked her to verify it.  So, in the middle of the tax season (shortly before the March deadline), she lost the ability to do efiling...  The only help I could offer was to do the e-extensions.  EFIN is administered by IRS e-services.  The phone service is quite accessible.  (I just incorporated and my corporation needs its own EFIN.)  In both times I called, the folks at the IRS e-services called me back (an offered option) - in about 40 minutes.  The folks at e-services are very helpful and effective.