There is now a rapid inspection regime. The CFM56 has been in volume production for some 35 years now, so I wonder why it is only now that an event which requires a campaign check has come to light.
There are differences between the fans of the different marks of the CFM56 (the 737 NG is the -7, previous 737s were -3, the A320 is -5, and those used to re-engine KC-135s and DC-8s were the -2). Furthermore, according to one write-up, the event engine had 40,000 cycles, 10,000 since overhaul (I'm a bit suspicious - 40k cycles would be a huge amount - I wonder if that's hours not cycles). At any rate it's a very high time engine, so it seems likely that we're looking at a wear-out mode - which may be unique to the CFM56-7 model.
At any rate the FAA has some explaining to do regarding why it's been sitting on a planned fan blade inspection AD for 8 months...