Turns out that the open-ended temporalCoverage thang is an open issue (and I may have correctly guessed the 'right' answer):

https://github.com/schemaorg/schemaorg/issues/1365

In a way what I learned with my 30 year-old AI degree was that meaningful semantic networks are hard ("is A", anyone?) but I'd have thought that some of these basics would have been nailed in a practical schema by now!