innews: snipped-for-privacy@w5g2000hsg.googlegroups.com:
We can have 6 digits on the side if you include multiple units although Southern region manages to identify its units by the last 4 digits careful not to overlap. No such luck with locos 87001, 67001, 47001,
37001, 27001 overlap on 4 digits admittedly less likely to overlap than 2 digits but you which which number manufactures are bound to pick for locos they make.The one good point about the Hornby system is that you can allocate free text as well as an address to a loco, text held on command station. So you could map the full six digit loco number to a 1-255 address, which is probably more easy to use than remembering the last 4 digits and Bachmann are doing the same with their system. 4 digits were all that is required in the US as that is all the digits they use to identify locos with duplicates between different rail roads.