Of course, the answer to the question of "how many can there be" is "as many as Topps wants, because they make the rules and they know we're just going to buy them anyway."
Here's my (not so) expert opinion:
I think Topps used the term "White Whale" on all of the printing plates from Triple Threads.
So I think this one is the Magenta plate:
Here is the Yellow plate:
And here is the Cyan plate:
Pretty crazy that 3 of the 4 have already shown up on eBay. This is my best guess, but feel free to tell me that I'm an idiot and that my theory is completely off.
the white whales issued by topps are cards made using printing plates as the top layer of a thick card.....some simply say white whale while others DO read white whale printing plate ....
while i can't confirm that topps packed out all 4 plates in each product i'm quite sure that all of them ARE made from printing plates....according to beckett's checklist , some products only have one white whale for a given card , though i feel this is simply another case of an incomplete checklist on beckett - i think it's similar to their stance on some of the late-90's printing plates which they listed as a single card with a print run of 4 instead of 4 colors with a print run of 1 each.....
as for the two glavine cards pictured , unless i'm going blind , i'd day both definitely do have a printing plate as the top layer .....
i don't have access to all my collection at the moment , but if i can get my hands on them , i'll try to get some scans posted showing a few more white whales for comparison....pretty sure i can offer up some both with and without the word printing plate used in the description on the card though it's clearly evident they are all the same...