Vitrified Paris Ware or Early White Earthenware Paris?

Could my white Paris ware be vitrified porcelain rather than white earthenware?
I don't think this question has been addressed elsewhere.

I have just bought some more straw-coloured Paris ware on trademe and have been trying to pin down dates on that and the Paris I already have. The new cups have a cursive Crown Lynn variant backstamp, so with the knowledge that both whiter clays and and the Crown Lynn stamp were used from 1948 I believe these new cups are made in that year. They have smooth sides rather than the typical Paris stepping or banding (although the saucers, 1943-50 backstamp, are banded).
http://www.trademe.co.nz/Pottery-glass/auction-744767534.htm

I find it odd then that my white Paris ware has Ambrico "Made in New Zealand" backstamps. 

The 1949 movie shows cups being made, either 753 or Paris cups that have the same shape as the 753s: whichever they are they are smooth sided, as a lot of the cups sold as Paris are. The same movie also has some 752 or 754 cups. My white cup and saucer have the banding of the early Paris ware albeit in just three steps. By 1949 technology had moved on.

Re-reading Val in "Icon" I see that Crown Lynn developed vitrified porcelain in the war years. My saucer and porridge bowl are fully glazed so I can't examine the body material. But the cup has an unglazed footring: it has the same sparkly look as the footrings of my vitrified coffee cans. All of my three white Paris pieces have use marks but none of them has any crazing. They are all very sturdy and I have no issues using the bowl for my breakfast.

I believe these white Paris pieces are vitrified: any comments?

All my Paris here:
https://www.newzealandpottery.net/t4662-more-ambrico-paris#16663

Page 18 in Val Monk's Icon mentions vitrified porcelain early on, so you are probably right Jeremy.

Thank you Ev. I will keep an eye out for more. Love my vit.

And it looks as though I have a new best coffee cup:

to the grinder ...

Hot coffee ... no worries!

---------
15/8/14
Alison Reid gave me these to work out what they are:
Clear glaze on white body, 43-50 stamps

The question is: are they white earthenware of vitrified.

The saucer is smaller, lighter, than my vit one and has crazing so I'm thinking E/W.
With the heat shock of hot coffee my vit cup showed no damage.

The plate has no crazing, but some knife marks. Still pondering.

A sticking point is that these are white and have Ambrico stamps but my most recent purchase of straw coloured cups has Crown Lynn stamps (although the accompanying saucers have Ambrico stamps).