There are Mk1,Mk2,Mk3, MK3.1, Mk4 and MK5/DC versions of the Churchill 5
MK1 Pre August 2012 has a single top brick ( baffle) which sits in a cut out in the rear bricks.
Mk2 August 2012 - March 2014 has two top Bricks ( one upper, one lower Baffle) and straight rear bricks.
Mk3 March 2014 - October 2018 has a single air control, two small top bricks ( baffles ) supported by a bracket
MK3.1 The glass in this model is 335mm x 318mm. There is no ash pan seal.
MK4 - Single air control below the door with a hammerhead lever
MK5 / Dual Control - Cast Iron Door and two main air controls below the door for primary and secondary air, as well as a third air lever for tertiary air.