User blog comment:B214/Volume 21 info & spoilers/@comment-26865730-20160408034729/@comment-26865730-20160409180243

Yeah, the different systems are a hang-up, but I'm guessing Ishibumi-san can write his way around it. I've also noticed he doesn't put out a lot of useless info and that all six left behind their Queen or Ace is just too concidental to be a coincidence.

Maybe not specifically a "Black Jack", but Ishibumi-san mentioned it only once and never again. Could have simply been background noise or had he already thought of this as a plot device back when the BS cards were first mentioned? Otherwise the part about them forming Blackjack hands was wasted information.

Also, I think Swampydrake99 is onto something about them not being needed for the sealing, but instead are needed for the rescue of their comrades without freeing Trihexa.