Simply incredible construction, and I enjoyed the gridfill immensely -- it's definitely helpful to enjoy logic puzzles too. I started the fill after getting only a handful of answers, by writing in all the possibilities for vowels, sudoku-style (so for E I wrote in a small 3x2 grid of letters in each of the three cells, for example). Some crossing entries allowed me to erase some of those options; occasionally all the options collapsed into a single encoded letter and I could use it to work backwards (eg I might see the second letter was a G and deduce the relevant letter of the answer couldn't possibly be a vowel, and that would help etc).
Is it just me that sees some ambiguity in the very last step though? The entry of "source"? The conversation here has been about the source of a particular quotation, but I've been considering the source of a noun instead. Rather than the "wrong information" disclaimer being about misattribution, I thought it was because the answer was very much unknown. (Maybe it doesn't matter, since the information would definitely still be wrong!)
Anyway, Cagey, that was wonderful!