We have a pipeline job (live branch) that's set up to build a certain branch - every 10 minutes it polls for changes. The rest of our builds are set up to do a multibranch pipeline for the other branches in our repository (which we do to work around the fact we can't set a job priority for our live branch to build it before other branches).

I currently have 9 builds for our live branch job in the queue because it polls for changes and sees a new commit in there which hasn't been built. Because there's no free executor at the moment, none of them have started so the commit hasn't been marked as "built" yet. The multibranch pipeline job doesn't do this.