all marzocchi forks are date stamped on the lowers, its usually between the disk brake mounts but can sometimes be found on the inside of the left leg, near to where the hub is when the wheel is mounted... i have seen a date stamp on both legs of the earlier marzocchi's, think its because of the arch being removable on them
*EDIT* your goin to be looking for a little circle of numbers (1-12) and the number that has a dot over it relates to the month they where produced. there is a number in the centre (01 for 2001, 02 for 2002 etc etc) this relates to the year the fork was produced. if the fork was produced towards the end of a year (from september onwards i think) the model year is the following one, e.g. the new 2012 forks are out and available to buy now