I have a size 46 1944 pattern ELC Irvin. I'm usually a size 44 and I bought it because it was on sale and because I wanted an Irvin big enough to wear a sweater. Based on this I would say I would say they are true to size. I have ordered a 1942 pattern Irvin from ELC, but this time in 44. I have an Aero prewar Irvin (44) and I think this is smaller in size than ELC.
I would agree with this. I have the other sale late war Irvin from ELC and its a size 44 and fits as such. It is the same size as my original size 5 Irvins. The best thing to do is to try them on. Gary had several on display at Duxford last week. He also has some 1944 pattern Irvins, which are rather nice, using smoother leather than on the two test jackets sold earlier in the year.