^ The only other reference point I have is a TCB Seamen’s jacket (which fits but I’ve never worn) in size 38 whilst my 30s jacket is size 42. Although completely different styles, they both feel of a similar size (ie both should have the same size label in them) if that makes sense.
I originally had a size 40 in the 30s jacket, which I wore for a couple of years but it just felt too small, particularly when done up so I sold it and bought a 42.
I only wear it as a summer jacket with a t-shirt underneath, it would be too snug to later with a sweatshirt or jumper, if I’d wanted to do that I’d have bought a 44. It’s a great jacket though, I’m very happy with it.