Hi Roberta,
I have been investigating all of those questions for many years. I recently added a request under the British & Irsih Glass forum:
Attention all MONART collectors ... in the hope of covering some of the ground once again.
To answer your questions, my understanding / observations so far are:
1. If there is any definite proof of an assumed Vasart item actually being a pre-war piece, then yes, some of the many other items might also be pre-war.
2. There are known pre-war Ysart canes that are used post-war in Vasart items and on through Strathearn and in "unknown maker" work, too.
3. The uv tests will work on any item that has enough clear glass to show a reaction. But for non-paperweights, it is often only by looking at the edges where clear glass shows that a uv reaction can be seen. But the uv reaction of pre-war Monart and Vasart items is pretty much the same!
4 a) For pre-war Monart non-paperweight items, the same canes were certainly used by all of the Ysart men. This is a simple consequence of their production routine where each of them had a particular role - with main shaping by Paul and finishing by Salvador.
4 b) I have evidence, from examination of paperweights, that a number of canes can be found in both Paul's and the other family members' post-war work. This strongly suggests that although Paul (and perhaps Salvador) had "personal canes" pre-war, they probably did get "shared". I suspect that when Ysart Brothers Glass was started, lots of canes, including some thought be personal to Paul, were just picked up and taken to the new venture. And ... Some of the canes in Vasart items that are said to be "Salvador personal canes" are also known in Paul's paperweights ... with the most likely explanation being that they are pre-war canes that migrated to "both sides of the family".