a harry potter-story ?

They moved the building by 11 houses? And (depending on numbering scheme) perhaps to the other side of the street?

Maybe they misunderstood the Gregorian calendar reform ?

This is part of the Phillimore Kensington estate.The late-Georgian terrace on the east side of Hornton Street was demolished in 1903 and the present terrace of a block of flats and 21 houses were built in its place with postal numbers 1-43 (odd) starting from Horton Place. In 1928 the terrace was renumbered 12-54 (even) with the new numbering starting with premises to the south of Horton Place.

Thanks, how extremely informative!