As far as I am aware the only signifcance in the numbers is for Prems, where the fist three digits indicate Prem and the forth digit indicates (or at least used to) annual or lifetime (1 or 0).

Back in the distant past Special Services told me this was in order for them to identify a Prem without easily and without the Prem having to state it or show a card - something which was either just not the done thing or not done for reasons on anonimity.