The smock I have is a "Ventile-esque" one made by SASS some years ago; the material is Ventile in all but name according to my reading the history of these, having followed up on some info. kindly provided by British Red who had one of the few real ones. During my Googling I found a good few images of this smock, and all of them show the label having been cut out of the garment; I have a feeling that this was because of the use of the word Ventile, which would obviously have had expensive consequences had these been sold under that name.
My smock is very definitely as high grade and close woven a cotton as other Ventile garments I've owned, I also have a couple of different windproof smocks of poly-cotton and of cotton gaberdine and this one is very much like the Ventile and not at all like the others.
Coincidentally, I put this and a few other waterproofs I use into a drier at the local launderette yesterday, forty minutes at medium high, and it seems to have restored the waterproofness of it very well, although it still doesn't stiffen up anything like other Ventile I've used, but it kept me dry all day today in quite heavy rain so I'm a reasonably happy bunny