Smokebox door handwheels/darts

[Rlangham]

On older photographs of NER engines (such as when in service, but sometimes seen in LNER days) handwheels on the smokebox door are often seen instead of the two 'dart' handles which seem almost universal nowadays. Was there any particular reason for some engines having them and some not, did it depend on when/where the locomotive was built or simply down to the crew's preference?

[Hatfield Shed]

Designer's decision (footplate crew were in no way authorised to alter design of functional components). As smokebox diameter increased, and with it the door aperture circumference, the force exerted by the tightening nut had to increase to produce an equivalent seal. I should think that accounts for the replacement of the smaller wheel - where it was used - with the larger lever, as locomotive development proceeded.