Typically (but not always) I end up with a start, a finish, some in between key points, and then have to write the rest of the story to link them together. Sometimes I've got the start of a story but not yet an end I'm happy with. Thus I have many part stories while I let my mind work on them. When something comes up that can fit in I add it to the story until I get the story done. Sometimes the story will blossom in my mind as a whole and it's written quickly.
We've discussed this before, and we work in a similar manner. I'll often let a story sit for months, as I work out how to make it work before I ever type a word. Like you, I'll have the beginning, an ending and various way points, but not all the connecting details. Often, I'll only know what happens next when I lay my head on the pillow and the next chapter's events play out in my mind. The ending of "Catalyst" is a prime example. I knew from when I first started that the MC would eventually die, I just didn't know how. It wasn't until I was wrapping up the second to last book that I figured out that detail, and I only fleshed it out as I got to it.
I'm not criticizing your technique, just stating that, so far, I've been unable to concentrate on writing two different stories at the same time. I'm not saying I couldn't, only that I don't trust myself to keep them separated. But, at any time, I have multiple stories playing out in my head, and I'll be simultaneously working on multiple plots. It's the putting the words in order that trips me up. I'm afraid typing out two different adventures at the same time will keep me from focusing on one fully. However, one of these days I need to try it to see how it works out.
By the way, it's been a long time since I've posted a story, but I've yet to hit a dry spell since I started writing several years ago. I get disillusioned, especially if I have to abandon or reject a story already in progress, which will shut down my creativity, but those moments pass as new ideas and new inspiration carries me forward. But what always saves me, if figuring out what the story was missing before, and then correcting it so the story works as it was designed.