I'm looking at 4 months data on JL874 PVG-NRT
Looks to me that only 3 days out of the 4 months
July 12th with a 9.42pm arrival
May 2nd with a 5.16pm arrival
April 3rd with a 5.22pm arrival
these will cause you to miss the connection.
anything arriving at Narita before 5pm JAL should hold the flight and the bags should make it also. I've done a 20 connection before (flight extremely delayed) and my bags even made it without sweating.
I'm thinking you are over worrying about this situation