In the 1920s the German mark went from three marks to the dollar to three trillion marks to the dollar in a very short time.

Judged against historical exchange-rate data for the German paper mark against the US dollar. True: within the 1920s, the rate moved from roughly 3 marks per dollar (single digits) to roughly 3–4 trillion marks per dollar within a few years at most. Mostly true: the hyperinflation reached about 4.2 trillion marks per dollar (in late 1923) in a short period, but the starting rate of about 3 is slightly off, or was from just before the 1920s (for example 1914 or 1919, rather than the 1920s proper). Mixed: the order of magnitude of the end point is correct, but the starting figure is substantially wrong or the timescale is significantly longer than 'no time'. Mostly false: there was hyperinflation, but the end figure is wrong by orders of magnitude. False: no movement of this kind occurred.

Set before the research began.

1. E1 Papiermark - Wikipedia Wikipedia

   “Between 1914 and the end of 1923 the Papiermark's rate of exchange against the U.S. dollar plummeted from 4.2ℳ︁ = US$1 to 4.2-trillionℳ︁ = US$1.”

2. E2 Measuring Worth MeasuringWorth (Lawrence H. Officer, exchange-rate dataset)

   “| 1920 | 57.1100 Mark |”

3. E3 Hyperinflation in the Weimar Republic - Wikipedia Wikipedia

   “The German currency was relatively stable at about 90 marks per dollar during the first half of 1921.”

4. E4 Cautionary tale from prophet of the unlikely Chicago Tribune · 14 January 2008

   “Taleb noted that during Germany’s economic crisis in the 1920s, the mark went from three per each American dollar to more than 4.2 trillion per dollar”

E1 shows the Papiermark fell from 4.2 marks per dollar in 1914 to 4.2 trillion per dollar by the end of 1923. That supports the claim's order of magnitude for the end point (4.2 trillion rather than three trillion) and a single-digit starting rate, though it was 4.2 rather than 3 and dates from 1914 [E1]. Within the 1920s proper, though, the rate was already about 57 marks per dollar in 1920 (E2) and about 90 in the first half of 1921 (E3). So the single-digit starting rate comes from 1914, before the decade, which matches the criteria's "mostly true" case.