I believe that there should be retests at least every three years or at a minimum, required, documented attendance of a code change seminar of either 8, 16 or 24 hours.
As you mentioned, there are facility "electricians" out there that just know what they need to get by and don't always do things right. We've all come in behind them to fix either related or unrelated problems and seen shotty work.
Also, here in PA, there are general contractors that will have people that they employ as their "electricians" that only know what they need to know to get by for wiring anything from warehouses to town houses.
It's a pet peeve of mine how we can get underbid by "contractors" that we're sure are not up on the current codes and there for cannot possibly do as well a job.(the first time anyway)
I, myself take every oportunity and encourage my employees to take every oportunity to learn as much as they can about the NEC and changes. Especially when someone is offering free seminars.
PS - I also believe that people 70 years old and older should have to retake their drivers test every couple of years also...but thats another topic.