I wouldn't doubt it a bit that after 1927, or when the Crayford-North Kent facility was downsized or closed, that they outsourced or subed the work. And it is possible even before then. Being somewhat devoid of maker's marks either they performed the tasks inhouse or subed the work to an "in the white state", or later in the process, and then worked off, or hid, the marks in the finishing. Liability/risk management and profit margins are the name of the game.

Kind Regards,

Raimey
rse