The creators of This is Spinal Tap, the most influential mockumentary ever made, have been paid almost nothing due to "creative accounting":

In 2013, Harcourt advised [Harry] Shearer to ask Vivendi for a complete statement of his interests in This Is Spinal Tap. Harcourt combed through the material that came back, and her conclusions were so shocking that Shearer’s response was as unprintable as some of his band’s lyrics. According to Vivendi, Shearer and his three creative partners’ share of total worldwide merchandising income from 1984 to 2006 was $81, and the total income from soundtrack sales from 1989 to 2006 was $98. That’s just dollars, with no zeros at the end. It was Stonehenge all over again: They’d expected feet and got inches.

The co-creators -- Harry Shearer, Rob Reiner, Michael McKean and Christopher Guest -- are suing for 400 million.