Your MZ3 is either 2003 or 2004 (MZ3 was used both years). MZ6 is definitely 2006, unless it does NOT have the upgrades (medium-jumbo frets, hotter pickups, 60th Anniversary emblem on the back of the headstock). I bet some MZ6 numbers will run in to this years (2007). Fender's usually do that.
As for the Dean, this is what I was able to find via Google:
From
http://www.vintagerocker.com/serialnumbers.html
"Dean guitars made in the USA follow a serial number pattern consisting of a 7 digit number with the first 2 numbers being the year of manufacture, followed by instrument production numbers. The serial number is found on the back of the headstock. Imported Dean guitars do not have year coded serial numbers and have to be dated by configuration and design."
Your best bet with the Dean would be to take some good pics and post them up on the Dean Forum.