Re: Ownership matters
original postcode boundaries areas(SW), districts(SW19) and Sectors(SW19 9) were matched to admin boundaries but these have changed, however postcode boundaries can not be changed to match because of the impact that this has on users particularly businesses who need continuity of Address across there stationary and advertising.
Unfortunately there is often an urban myth that postcode and admin boundaries match and when they don't a mistake has been made. In your Case the council is wrong and the Royal Mail is right but good luck in convincing them.