My late mother had a two billion mark stamp from Weimar-era Germany, though I see from Wikipedia that's not even close to the record (they have a picture of a five billon mark example in their article).
It had gotten so bad that they didn't even bother printing new stamps; they'd just overprint the new value on the old stamp in black ink.
It had gotten so bad that they didn't even bother printing new stamps; they'd just overprint the new value on the old stamp in black ink.