I believe the the first Sun XCD derailleur was released in 2014. This was the Sun XCD (SXRD34M), an all silver model, notably with a silver pulley cage.
I further believe the the second Sun XCD derailleur was this one, the Sun XCD (SXRD51MB). It has a black pulley cage (possibly this is specified by the 'B' in the model number). Aside from the colour of the pulley cage, I am not aware of any other differences.
Both were, fairly standard, long cage, microSHIFT models rebranded as Sun XCD. Strangely neither derailleur was from microSHIFT's most prestigious groupsets, but, rather, were more 'upper-middle' market models. They were nicely finished and tastefully branded, but they had steel inner parallelogram plates and weighed in at a chunky 232g.
Decent enough - but I had quietly hoped for more.