I know this is an old thread, but I am 99% sure that the three digit date code format is YMM, not MYY, so the OP's Netvista with a MFG Date of 305 would be May 2003, NOT March 2005. I venture to say that pulling the hard drive from a few of the machines and looking at their dates will confirm this, so long as the HD is original to the machine.
I guess they figure you can determine the decade easy enough based on the hardware, so no need for two digits for the date. I ran into a Netvista sometime back that was pretty old, and the MFG Date was 212...pretty obvious that was December of 2002, NOT February 2012.
I actually use a similar format for assigning ID numbers to PC's...only had five digits to work with, so I use YMM##, for year, month, sequential number (never purchase more than 12 in a month). This way, I can easily determine the age of a PC by it's ID number. Hopefully, by the time a decade passes, none of those PC's will still be in use.
Of course, the Majority of the Netvista's I come in contact with came from a large purchase my employer made about nine years ago...most all of them say 303, so I am VERY confident they date to March of 2003. LOL
Hope this helps someone...