Although the paper was holding up, unfortunately the cellophane underneath it wasn't:
I therefore decided to open the seal and take a look inside. The seal was for tax purposes, by the way, as there was duty to be paid on packs of playing cards back then. Here's the duty seal and some kind of, well, I guess inspection card, that fell out when I took the cards out to look at them.
Here's the entire pack:
So, I'm the first person ever to look at this pack since it was sealed up. I didn't shuffle the cards or anything, I just laid them out in the order they appeared.
Why is the Two of Spades between the Ace of Clubs and the King of Diamonds?