Older drum cable setup persistence
That gap matters more than it sounds like it should. A door installed in the early 60s or 70s often still runs on older drum-and-cable setups that don't match what shipped standard by the late 80s. Manchester's stock, being closer to the newer end of the city's range, is more likely to have factory-standard extension or torsion cable runs with fewer of the odd retrofits you find on the oldest houses in town.