When fiction slides into your footnotes as fact

This afternoon, I was doing what passes for academic multi-tasking--i.e., reading a scholarly essay collection while eating dinner--and found myself yelping in pain every time a well-known historian of religion cited "Osborn W. Trenery Heighway's" Jewish conversion narrative Leila Ada as a straight-up biographical source.  Because I'm afraid it isn't.   I've previously registered my suspicion that Francis Edward Paget's A Student Penitent of 1695 should not be touched with the proverbial ten-foot pole, or even a twenty-foot pole, until somebody verifies that the letters it claims to reprint actually exist.  (For some reason, neither Google nor Typepad will let me call up the post right now, but while the people in the book are real, the letters are so straight-up Victorian in prose style that surely they ought to ring alarm bells.)  At least one doctoral dissertation mistakes Emily Lawless' With Essex in Ireland for an actual diary. This doesn't constitute an epidemic--quite the contrary, there are just a handful of examples--but it's worth noting that the books causing all the trouble are precisely the ones that claim to be some combination of memoir, journal, or epistolary collection.  I have similar questions about an "autobiography" I briefly mention in an article I have forthcoming next year (my verdict: the book sure acts like it's a novel--but while its relevance doesn't have anything to do with its reality in this instance, I'm still not sure if I should drop it anyway).  Some nineteenth-century things are not what they claim to be, and we don't always know what they are until it's too late...