In order to test some of the suggestions given here, I did some more work in the shop today. I started by grinding the chisel back a bit, probably a mm as suggested by Patrick. I then put a small back bevel on the chisel and proceeded to chop some pine. To my subjective eye, it appeared that the edge lasted longer.

Since I had changed two parameters I couldn't tell which one might have contributed to the longer life, so I took another Narex chisel and only did the grind back on the bevel. That one seemed to hold an edge longer than in my original test. These results are completely subjective - I have no way to objectively measure sharpness or how long an edge lasts - but subjectively, I'd say that the edge lasted longer. I did use a 10x loupe to examine the edges after chopping for a fixed number of "chops".

It was during my examination with the loupe that I noticed something unusual on the 16mm chisel. There is a defect in the steel.
2018-02-21Narex001.jpg

Here's a closeup of the defect
2018-02-21Narex002.jpg

The edge could be sharpened to a sharp, smooth edge but as soon as I used the chisel, the edge broke at the defect area.
2018-02-21Narex003.jpg

And here's a closeup of the edge after use, showing the "chip" in the edge.
2018-02-21Narex004.jpg

This is not what I was getting last time - last time I was getting a rolled edge - so this problem showed up because I ground the edge back a bit. I'll probably have to grind the edge back past the defect.

Anyway, it seems that grinding the edge back a bit improved how long the edge lasted. I'll keep using the chisels and see if my opinion changes when I'm doing real dovetails.

Mike