I began simply writing independent short stories involving some common characters. It was only a half dozen stories later that I realized I was writing a "novel." By then I'd had a number of the stories published as stand-alone works, though this doesn't seem to be an insurmountable problem to getting the whole considered.

I've begun to call the whole a "story collection" rather than a "novel." There are a number of publishers who take story collections, and it's often a requirement that 40% of the pieces in the collection be previously published for the whole to be worth consideration. I think I'm in a good place.