I think the people to ask about more double seals being in existence would be Lee Asher, Bill or D&D. Those that have seen or possessed more then a few dozen JN's.
That's not even necessary. If you do enough digging on eBay and around here, you'll find enough cases where a manufacturing error increased the perceived value of a deck and that deck was sold at a premium compared to the standard, "perfect" version. It's not about what an expert collector thinks that determines a deck's value, it's about what all collectors even vaguely interested in owning a deck think that determines value.
The thing that makes such decks valuable is their rarity. An accidental double stamp sealing a deck is not much different from an accidental double-struck coin from the US Mint - it's an accident that occurred which made that double-stamped deck more rare than the others with only one stamp. Something like accidental DAMAGE, on the other hand, is NOT considered valuable in any way by anyone - like a box of cards that fell off the table and has a dented corner.
Personally, I think it's a bit silly, but anything's value is what people are willing to pay for it, and people are willing to pay a premium for decks with manufacturing errors despite the "Q1" quality control employed by USPC for most custom deck designers today.
Another thing to bear in mind - if the error is COMMON, like the smeared ink on the original Fontaine decks' boxes, affecting almost the entire print run, then there's no additional value attached - it's not a rarity, not unique in any way. If a few decks survived the print run without getting smeared, THOSE would be the valuable exceptions.
Here's another way of looking at a similar circumstance without having to compare it to "government made" errors in postage stamps or currency - Three examples from the universe of "Star Wars" memorabilia.
1) When Kenner first started making the action figures, they released a "Jawa" figure that had a cheap-looking vinyl cape on its back with armholes to keep it in place. Shortly into the production run, a decision was made to replace the cape with a sewn-fabric cloak to give then an appearance closer to what they looked like in the film. That Jawa figure with the cheesy vinyl cape, mint in package, now sells in the four figures and many attempts have been made to counterfeit it.
2) During the TV show "The Star Wars Holiday Special", broadcast between Episodes 4 and 5, an animated short was shown with a new character, a bounty hunter now known as "Boba Fett". Around the same time, Kenner held a promotion where you mailed in the proofs of purchase from I think six action figures and you would get a Boba Fett figure in the mail. The original design called for the rocket pack on his back to be equipped with a grenade launcher - in this case, a spring-loaded mechanism for firing a little red missile and launching it across the room. But between the time the offer began and the first shipments were being made, a competing franchise, "Battlestar Galactica", had fighter ships that had pretty much the same firing mechanism - and at least one case of a kid firing the missile down his throat and nearly choking from it was reported. The missile-firing version of Boba Fett never made it out of the prototype stage - the missile was now permanently attached to the jet pack and the spring launcher was removed and replaced with extra plastic to keep the missile from being removed. It has to be one of the most counterfeited pieces of Star Wars memorabilia, but prototypes are worth princely sums each. They were unpainted, never placed in retail packaging and it's estimated that only perhaps a half-dozen genuine figures exist.
3) Topps licensed the rights to manufacture "movie cards" for the Star Wars franchise back in the '70s. They were sold much the same way that sports cards of the period were sold - wrapped in a waxed paper with a handful of randomly-chosen cards and a stick of cheap but tasty bubble gum dusted in starch to keep it from being sticky and adhering to the cards or the wrapper. It's hard to find unopened examples of these packs because time is not very kind to bubble gum that's not sealed airtight! The first Star Wars film generated five series of these collectible cards, each with 72 cards depicting movie scenes and promotional stills, and some were packaged with a sticker in the shape of a letter with a Star Wars character depicted in the letter - the idea was that kids would use the stickers to customize their notebooks, bicycles, bedroom, wherever. I can't recall which series it was, but there was one instance where a card had to be replaced. It depicted See-Threepio walking down a dim staircase into the Lars homestead - but because of the lighting and actor Anthony Daniels' position, it looks like there's a shiny golden phallus protruding from the droid's codpiece! The replacement card is of the same scene, but taken either a few frames before or after that pose, where the lighting didn't create such an effect. I don't know how many "phallus pose" cards were made, but they do catch a slight premium over the replacement card in the after-market.
I'm coming back from my tangent now, but my point is that yes, such rarities exist in the collecting world, and not just those who collect coins, bills and stamps. The people who collect such items do actually put a premium on things made in error, particularly if they're scarce.
