I've got quite a few that are above week 52, all are late 1960s designs with a prefix starting 9 or 09 (from several factories), I suspect it's due to the change in paint colors & IEC changes (for mains powered TE), for 1960s designs made post 1970, i.e. not a big enough change to give a full prefix code change.
The country code list is missing E for Bedford, England, with U being South Queensferry, Scotland, both in the UK, the E = England code isn't too common, as they were only there a few years before moving to Scotland.
David
factory