IN THE EXTREME
Do not adjust your computer screen. No need either to rush out for new glasses. This is basically just Hradcany collecting in the extreme!
And nope, they're not unique proofs.
As far as I know it's just printer's waste, donated to Czechoslovakian philatelic societies by the printers way back in the 1920s (if I remember rightly).
A colourful aside to the main thing. And there's even various designs printed on top of each other.