comments:
Three_Twenty-Three posted on r/lovecraft7w
I have the first (1994) and second (1998) editions of the one from Daniel Harms (his Encyclopedia Cthulhiana, which are apparently now worth ridiculous amounts of money on Amazon), and they served me well in the days before we had a Lovecraft wiki and instantly searchable texts in H.P. Lovecraft Archive. Neither of those links appears to be the book you described first, which is An H. P. Lovecraft Encyclopedia by S. T. Joshi and David E. Schultz ( https://www.amazon.com/H-P-Lovecraft-Encyclopedia/dp/0313315787 ). This also looks like an excellent book, although I think it contains a lot more about Lovecraft the person than the one by Daniel Harms.