Thank you @merefield for that thorough yet concise reference. The article was a terrific primer on the subject which I will surely re-read many times.
What I’ve learned so far (since initiating this Topic) is how very important it is to be proactive and informed, and to add a license to every. single. thing I release!
“Permissionless Innovation” is completely out of control. And let us thank our lucky stars for that.
I’ve owned what has turned out to be a consequential technology patent since 2001. My partner (the inventor) and I made the carefully considered choice to (instead of monetizing it as proprietary) very publicly release the full technical specs, in the most rigorous standard of detail, and in the most openly and widely accessible place, because we wanted it to have the best and soonest chance for widespread adoption.
Thankfully, we succeeded. Just as we intended, our invention got noticed and put into widespread use for the good (not all may agree “good” 
) of all humanity. I credit the US Patent system (“the people’s public repository of new and useful ideas”) for enabling this for us.
While patent law is one of the murkiest and least settled areas of law, history teaches us, time and time again, that permissionless innovation is a fundamentally necessary enabler of progress.
My reading of the Häußge primer reassured as well as enlightened me that the guardians of open source have provide us with the best possible “best practices” given the times and circumstances.
I also agree with @yanokwa that the responsible course of action in this circumstance is to
contact the authors and ask them to comply with the licenses of their dependencies and put a license on their own code. If they don’t respond, I wouldn’t use their code.