Plympton and Plymstock were originally separate towns but both were incorporated into Plymouth with a boundary extension in 1967. From memory I think this was achieved under a private axt of Parliament.Administrative boundaries change over time so I don't put much stock in them. But best of luck to anyone wanting to get the boundary of Exeter widened to include the larger travel to work area.
Bristol City were originally in Somerset. Grimsby are in Cleethorpes.