For what it's worth, this is the response I received from Track Shack/rD when I asked whether a certified race had to be a course/race specifically certified by a governing body (like USATF):
"In identifying a race that meets the proof of
time requirement, there are two criteria you want to consider in addition to
being the required distance within the timeframe.
1. A certified race. If it is not certified, then it needs to be one
step short of that, which is a measured course. The course has been
measured with specific measurement devices to confirm the course distance.
For example, you want to ensure that you are running a 6.2 mile race not a
5.8 or 6.5.
2. We do not accept self-timed, training or virtual runs. The race
needs to be timed by race management and that typically means with a chip or
tag device. The race management will report to you your finish time and
display results on a website where it can be verified."
Still doesn't totally clarify what "certified" means, but it seems like if you submit a PoT for an organized race that posts timed results online, that should qualify.