I have one I'm selling ( a Thelma ) and it's marked as 40. I think is a 12 so am selling it as such .. I believe they say it equates to a 14 but I don't think it will fit a lot of people who say they are a 14. ( if that makes sense ) .
I have just bought a Didriksons coat "Alba" I am a large size 10 and ordered a 38, it fits great and can prob layer under it. I think if you order your normal dress size you will be fine as they are true to size now, whereas they used to be on the big side.