British Heavy Weapons Platoon: Early War possible?

So full disclosure, I don't actually play Bolt Action but I dip in and out of it hobby wise and I've recently started getting into Very British Civil War as a project. That out of the way...

I just today bought the British Heavy Weapons platoon box, the one with the Vickers, the 3-inch medium mortar and the 4.2-inch heavy mortar, because A) I want it for my 1930's era British army, and B) it was relatively cheap at the FLGS.

Now it does say on the side that it's only really suitable for the Mid to Late war period (1942 to 45), but looking inside, apart from a few of the later period Mk.III helmets on the sprue, I'm honestly stuck on how this kit CAN'T be used for the Early War BEF and home defence/Territorial Army ala Operation Sealion or even in use for VBCW.

Can anyone tell me if I am horribly off base with this comment, or am I not that far off the mark that using not using the Mk.III would make the difference?