Here are my dots. Can you see the pattern?
Lexmark C530 Serial Number 9416FX1 (rendered in Photoshop to show dots visibly)
It's ridiculously obvious. Here are some rectangles colored over the pattern:
This really makes the pattern pop out. The dots are in a 21x8 matrix. The pattern is always the same - patterns from previous prints are identical to this scanned and rendered image. Therefore, it's impossible that date information is encoded into the pattern on Lexmark printers, just serial numbers.
I was on campus today, and found two more Lexmark color laser printers.
Lexmark C752 - Serial Number 940FNX2 (rendered in Photoshop to show dots visibly)
The green boxes are separate occurrences of the pattern; they cover the entire page just like my printer.
It's harder to see dots on this page because the print quality was poor; I am sure both of these campus printers have printed thousands more sheets than mine. Because the clarity of the pattern varied, I had to draw a massive grid to make sure I wasn't missing any dots from one square to the next. I was careful to ignore "noise" and only focus on repeating dots.
Lexmark C760 - Serial Number 940KG8H (rendered in Photoshop to show dots visibly)
I put everything into Excel to try and make sense of the patterns:
I'm temped to think that since the grid is 21x8 on all printers, and each serial number is seven characters, that each character is encoded by three columns of the pattern. For example, because the first six columns are identical on all three of the printers I've tested, the first three columns could mean "9" and the next three could mean "4".
I haven't had the time to really thoroughly check it out, but here's the information for the world to see.