I am struggling to find any references or documentation detailing the model nomenclature of Optiplex GX745 USFF models.  What is the difference between a DCCY or DCNE model?

I searched the Dell site, this forum, google'd and even called Dell but unfortunatley came up with nothing.  Using the Service Tags in the warranty status page only tells me that they have different parts and I have no way of checking all the model types.  In other words, I only have Service Tags for the DCCY and DCNE but I do not for the DCTR or DCSM models.

Does anyone know the nomenclature summarizing these four-letter model numbers? DCNE, DCCY, DCSM, DCTR.  Basically, what do these mean and what am I missing?

Thanks in advance.