Rolex has consistently manufactured more than one seriel letter prefix at a time..
There is no proof that they stopped producing/shipping "D" models when the "Z" models started appearing in the marketplace..
Likewise, we know that "M" is the latest, but there is nothing to prove that they have ceaased production of "Z" models......or even "D" for that matter..
It's a guessing game. These lists are based on invoices that show the earliest and latest dates.
I would bet that in the future, these "lists" will show that "D"s were around from late 2005/2006 to 2008, "Z" from 2007 to 2009, and "M" from late 2007/2008 to 2010.