The 'Upstream build that triggered this job' option provides a feature named 'Use "Last successful build" as fallback'. It would be great if there would be also something like 'Use "Last successful or unstable build" as fallback'.
This would be handy e.g. if you have a long running job A which is unstable and the artifacts of job A are re-used in another job B. But this job B is WIP and needs to be re-triggered multiple times (manually) and you don't want to re-run job A until you get a "successful build" but instead just fall back to the latest stable or unstable build.
Thanks for the Copy Artifact Plugin!