I have all of them except the Mary Westmacotts and "Come Tell Me How You Live".
When I was a teenager in the 70s, my mother bought me the Hamlyn "Crime Collection" series with three volumes in one. These contained all the novels and short story collections available at that time.
I bought copies of the novels and other collections brought out after the series finished.
Unfortunately, I lent one of my "Crime Collection" books to a friend and she lost it while moving house. I am still cranky about that more than thirty years later. I had to go out and replace the three stories that had been lost.
Now I very rarely lend books to anyone.
I have had Poirot's ABC Murders and EvilUnder The Sun on Video for ages, I managed to get my Favourite Episodes singularly and 2wo others on 1 DVD but had to buy The Clocks with 3 I didn't really want.
I have the same way of Choosing to buy a Book that you do MarcWatson-Gray, If I don't like the Blurb on The Back, I might not buy it or as I bought the Set Of ACs I read them 1st time round sometimes reading the ones with the best synopsis earlier than others and sometimes leaving the best till last but now I am re-reading them in Chronological order Missing out the ones I dislike.
I have all the novels and plays in paperback, some of them (1st ed USA versions) in hardback, a few 'movie-tie-ins", plus I have all the films and BBC audio adaptations on cd & dvd, plus several of the books on cd (ex: Hickson's readings of the Marple short stories) . Plus 4 or 5 biographies, special encyclopedias on Christie (ex: Christie A-Z) and about a dozen playbills of the shows from the 1940s up to the present, I am a Christie enthusiast !
I have all of them, I have the ones I will never read again on the Bottom Shelf and I have The Joan Hickson Miss Marple Video's on the Middle shelf, The rest of the Middle Shelf is taken up with some of my Favourites, I intend it to be for Capers like The Bundle Books and Why Didn't They Ask Evans and The Man In The Brown Suit but it could also have my Favourites like ABC Murders, Cards On The Table, A Murder Is Announced.The Clocks, Sleeping Murder 4.50 From Paddington, N or M and Partners In Crime, The tp shelf is in Chronological order not counting the ones I am done wth and as I finish the one on the far left it goes onto perhaps the Middle shelf but probably nearer the left of the bottom shelf, The Poirot and Miss Marple short story books apart from The Thirteen Problems.