I believe
The M55-E0 is the 2017 model. Has 32 local dimming zones. I have this model and it is excellent contrast.
The M55-D0 is a 2016 model. According to my research the 2016 model had 64 local dimming zones.
According to a review site, the 2017 model scored a 7.0 on local dimming (on a scale of 10)
The 2016 model scored a 8.0 on local dimming. I'm not sure most of us mere mortals could determine the difference.