Rarity of Paul Ysart Crown weights ... I don't have one in my collection, so they must be rare.

Actually, I have bd on several over the years but so far have not been the high bidder. There were several offered in the two-part "Parkington sale" at Christie's, London in 1997/8. Since then they appear occasionally in various auctions, through specialist dealers and in eBay.
I think there are probably more PY Crown weights from the Harland years (70s) than from either the 30s-50s or the 60s. The rarest may well be versions from the 1930s that have a very low dome, one of which is illustrated in the "Bergstrom book" and another I have personally viewed in a collection.
I agree that the label on the eBay one is most probably the white one with black letters. An example is shown in
my artcile in Angela's Glass Musem (but note that my pic shows the label as a "patchy" blue - which is actually the colour of the weight showing through the label which has become thin through wear.