This is true.
I agree with all of this to a point. But yeah, there could have been an in-between story. Afterall, he wrote The Magician's Nephew twice. The first version he wrote, he shelved, then he wrote The Last Battle, and then The Magician's Nephew, version 2, if I'm not mistaken.
That said, there are shows and movies that I don't mind having more and more of. At all. And no amount of additional stories takes anything away from the original. I say that because there have literally been hundreds of Star Wars stories, in films, TV, comics, books, with more new stuff releasing every month. I won't (and don't) like it all, but I don't have to.
There could be more Narnia stories set exclusively within the world of Narnia, like The Horse and His Boy. That's something that HarperCollins Publishing once explored. And there was also an author who did write an 8th book... he published only 100 copies of it (probably a minimum for a run) and only gave copies out to his friends and family. It was called The Stone Table, and it was about Susan Pevensie, if I'm not mistaken.