I updated the list of fictional footnotes with more information on Don’t Ask (1993) by Donald E. Westlake, which I just read (it’s a Dortmunder):
Two chapter headings have footnotes that identify them as “Optional—historical aside—not for credit.” Chapter six mentions a street with “a whole block of taxpayers.” This is footnoted: “A temporary structure, commonly one story in height and containing shops of the most ephemeral sort. Constructed by owners of the land when a delay is anticipated, sometimes of several decades’ duration, between the razing of the previous unwanted edifice and the erection of the new blight on the landscape. Called a ‘taxpayer’ because that’s what it does.+” The second footnote, indented under the first, says, “Didn’t expect a footnote in a novel, did you? And a real informative one, too. Pays to keep on your toes.”
The t.p. verso of my 1994 Mysterious Press paperback edition has this:
Enjoy lively book discussion online with CompuServe. To become a member of CompuServe call 1-800-848-8199 and ask for the Time Warner Trade Publishing forum. (Current members: GO:TWEP.)
I called the number but got a fast busy.