I am reading through the Underworld Sourcebook and just noticed the chapter heading Seoupla Rings. It uses the same spelling in the headers of all the pages in that section. I did not find any errata on it. Or did people not really read the book? Or it was brought up long ago and I missed it?

That was brought up a long time ago. The author and editors were both dyslexic.

For the record, it's not spelled "chemestry," either.

Sorry if I ever misspelled chemistry. I definitely will try not to.

Back on topic, I probably missed it since I did not get online until 3 years after Underworld's release.

Not you, the SR dev team. I can't be the only one that remembers the "Chemestry" chapter of M&M.