Advisor's/University's rights in the PhD/MSc alumni's research projects and publications
I am currently returning now to a thread of work that I started as a PhD student many years ago, but have not had opportunity to work on since then. I will not be including my advisors as authors on the new papers that result, because the work goes beyond anything that we worked on or discussed during that project. So there's no direct overlap there, and thus they have no intellectual investment in the project.

I would argue that you would continue to include the advisors if they are actively collaborating with you on the current work that you're publishing—or if the original work that you're publishing was done while you were under their supervision. 

Of course, you do need to cite the previous work that you've done on the topic as part of placing the work in its appropriate context within the larger experience. You should also be notifying your advisors of your recent work because it's the smart thing to do—you should always keep mentors apprised of your ongoing research activities!