In reply to AndyRoss:
For DMM, modern kit seems to have a code such as 113441234A, this being YRDAY####*(# being serial number, * being a manufacturer mark), some smaller gear, such as nuts have 14A on them, 14 being the year.
Petzl seems to be similar, with first 2 digits of serial number being the year, and either 3 figures for day of year or one figure for month of year afterwards.
Problem is when I hae gear from DMM, Wild Country, Petzl, Clog, CAMP etc it all gets confusing haha