It's a true story! (Or is it?)

I admit that I've been grousing a bit about F. E. Paget's A Student Penitent of 1695, which I fear I did not receive in the state of mind that Paget intended.  The most interesting thing about the book is, in fact, the question of what it is: an edition of the letters and commonplace notebook of Richard Graham (1679-97), son of the Jacobite Col. James Graham (or Grahme)? Or is it a novel based on those letters? Or a "factional" combination of the two, drawing on both seventeenth-century sources and Paget's own inventions? (There's no doubt about Richard's existence or the manner of his death--the aftereffects of toppling out a window.)  The authenticity of the letters appears to rest on Edward Plumptre's account, itself based on verification from Paget's family--but, somewhat frustratingly, he reproduces none of the originals, merely an example from Paget's text. There's no sign that Plumptre saw the letters himself.  Moreover, every single reference I've seen to the original texts goes back to Paget, right down to the late twentieth century.  This is true even of Josceline Bagot, who owned Levens Hall (where Paget claimed to have found the letter) during the Victorian period, and who only mentions Hugh Todd's correspondence (that is, the Vicar of Penrith, Richard's tutor) in the archives. The late-Victorian Historical Manuscripts Commission report on the MSS at Levens Hall has quite a bit to say about JG's correspondence, but makes no mention of anything by Richard.  Hunting through the various online UK manuscript registers, whether national, Cumbrian, or the BL, turns up nothing, even using multiple variants on "Graham."  I don't have access to Paget's Ashstead and Its Howard Possessors, which enumerates JG's correspondence--perhaps there's a mention there? Meanwhile, Paget's case for authenticity comes with a somewhat eye-popping description of his own text: "...gaps have been filled up, and there are many omissions, additions, alterations, substitutions, yet nothing affects, in any essential point whatever, the real history, or tampers with the sentiments and opinions expressed in the original documents. Only the language has been modernized where it seemed expedient, and the medical details have, for the most part, been suppressed or generalized" (xi).  That's before we get to "many of the letters are given just as they were written, or with no more change than the insertion of a word or two here and there, by guess-work, where the ink has so faded as to have become illegible, or the paper perforated by book-worms" (xi).  This is almost a parody of the found manuscript trope ("hi, I've got these great letters, and I've reprinted them just as I found them, if you don't count the fact that I've rewritten them entirely").  In any event, I'm mildly intrigued by the backstory, if not by the book.