I have a theory about this, which most probably may be wrong!

There were a few maps which were not updated regularly, for example the ones with Sensis data and the nuvis would have a "maps out of date" nag screen. So, does that nag depend upon the year and quarter in the map name or the date of publishing within the map? If based on the map name, then the nags would be deferred by at least a year or so, thus keeping the number of irritated customers down. Btw, the maps published from Taiwan (TWN, IND, SG/MY, TH etc) don't have this dating anomaly.