Jenkins – Copying artifacts from multiple upstream jobs at join in Jenkins

Is it possible to have a Jenkins Job with has been triggered by the Join plugin copy artifacts from multiple upstream jobs?

I'm trying to set-up a Jenkins configuration with a "diamond" of jobs: my-trigger runs and spawns two jobs, my-fork1 and my-fork2, that can run concurrently and take varying amounts of time, and the Join plugin sets off the job my-join once both forks have completed.

Each of my-trigger, my-fork1 and my-fork2 creates and fingerprints artifacts (say, text files).

I want to copy the artifacts from each of the upstream jobs in my-join using the "Copy artifacts from another project" tool, with the "Which build" parameter set to "Upstream build that triggered this job". However, I see output like this in the console of my-join:

Building remotely on build-machine in workspace /path/to/workspace/my-join

Copied 1 artifact from "my-trigger" build number 63

Copied 1 artifact from "my-fork1" build number 63

Unable to find a build for artifact copy from: my-fork2

and the job fails. In this case, my-fork2 finished first, so my-fork1 triggered the join step. I believe that that means that my-join only has record of my-fork1 and my-trigger as being upstream. If my-fork1 finishes first, then my-fork2 kicks off the join, and the job fails when trying to copy from my-fork1.

If I change the configuration to copy the artifact from the build "Latest successful build" then the build succeeds, but my-trigger may run many times in succession so there would be no guarantee that my-join is joining related artifacts.

How can I get the join step to copy artifacts from multiple forks upstream?

Note: the second point of this question seems to be asking the same thing, but the only answer there doesn't address it, and has been accepted.

Thanks
tensorproduct