Sorry for the really vague title, I think it's vague because I'm not quite sure myself what I need to know but just wanted to float this past you more experienced world-builders to see if anyone has done what I'm currently doing, or sees any issue with it.

My main WIP is a novel (probable trilogy) set on Earth and in a fictional world (which are linked by a dreamworld - not important for this question just providing extra info!). I am probably halfway through my first draft and realised that I'd written many of the Earth and dreamworld-based sections and very little of the other world, so I came up with a short story idea which has really helped me with my world building, and it's developing into something I am quite pleased with and may submit for publication (after much polishing). Then, I had a couple more short story ideas.

Any advice in this regard - if something got published (big 'if' of course), would it be self-plagiarism if I were to then include any of the detail from one of the short stories in the main novel series? Should I be avoiding or embracing this urge? Has anyone done similar?

Thanks in advance