It looks like someone reused an empty booklet with a refill of sheet stamps, done carefully with the stamps folded face to face so the gum was against a glassine interleaving.
Otherwise there are just to many production errors to explain: stamp direction, 2 panes face to face without interleaving, full perforations, etc. While the stamps may appear "stuck" in the booklet, I suspect you will find they are not stapled into the booklet at the end. Count me as very skeptical.
It does not take any staple removal to peek under one of the left corners to see if the stamps are fully stapled-in or are (my guess) just folded and jammed in tight enough to have become stuck over time simulating being "bound-in".
Maybe just for fun? A friend of my father, everytime he went to DC got $100 of crisp new $2 bills, squared them up nicely, and then stuck a piece of cardboard with rubber cement on the end. Then, when he went into a store to buy something, he'd pull out this pad of fresh, new, crisp $2 bills, tear off how many he needed, leaving the clerk dumfounded.