Strollers is a type card I'd love to stumble across.
Although I've published it repeatedly people and especially graders do not seem to understand that there was a W580 parallel tobacco issue in Siam [Thailand]. Here is a side by side of a Siamese card [L] and a W580:
Besides the obvious cutting differences--the Siamese cards are machine cut--the other key differentiating factor is the card stock. The Siamese cards are printed on a thin white stock with a finished front and back, so both sides are white-ish and there is some gloss to the fronts. They feel like E120 and related E issues. W580s are made of chipboard with one side finished and there is normally no gloss apparent. W580s are also nominally thicker and coarser than the Siamese cards.
A final good indicator is where the cards come from. The Siamese cards were almost certainly a British tobacco issue for export ciggies, so they are often found from UK sellers. I've also picked up several groups from Thailand and Malaysia and Singapore.
In terms of rarity, the Siamese cards are many, many times more difficult to find than the W580s. I would classify them as equivalent in rarity to T219 Red Cross. They are the sort of card you stumble across.
Hunting these down in eBay is also tricky. In scans it is often tough to tell whether a card is just really nicely cut or a Siamese card. The grading companies do not know the difference, though I plan to send SGC and PSA an explanatory memo when I post a version of this to my blog.