Introduction of Mark 2Z/A/B/C stock

[Sun Chariot]

I'm sure Mk2B coaches lost the middle door.

Mk2C had passive provision for aircon.

Mk2 and Mk2a:
TSO had narrower passenger doors at outer ends and also middle of bodyside, between saloon windows 4 and 5
FK had narrower passenger doors at outer ends; its corridor side had narrower door, between windows 3 and 4.
BFK, BSK, BSO had narrower passenger door at each end of saloon (i.e. one outer end + middle of bodyside).

Mk2b and Mk2c:
TSO, FK, FO had wrap around doors at outer ends but no door in middle-bodyside.
BFK, BSO had wrap around doors at outer ends and narrower door in middle-bodyside.
MK2c early batches had a Mk2a/b style "vent" toilet window; Mk2c later batches had fully sealed window (vent above it).

Positioning of underframe equipment altered between each variant, too.

 

[matchmaker]

MarkIICs were easily distinguishable because they had wrap round end doors.

"Plain vanilla" MarkIIs were distinguishable from MarkIIA and MarkIIB by the absence of air brakes, except for the Scottish push pull vehicles, which were distinguishable in other ways.

Of course it was always possible to cross check the vehicle numbers!

Knowing which sets were air braked and which were vacuum braked was very important operationally.

If I recall correctly, Mk2s couldn't be dual braked, although Mk1s could.

 

[hexagon789]

If I recall correctly, Mk2s couldn't be dual braked, although Mk1s could.

Yes, though I understand one heritage line may have created a dual braked Mk2 in a fashion.

They never existed in BR service though.