I think these are all unique connotations and I have heard "service" applied to all of them.
The goal here is not to try to correct the world's usage of the term, but to structure a workable metamodel. I continue to think that we achieve clarity through qualification; I am going to try to avoid the term "service" and specify instead whether it is a service outcome, service act, service offering, or service system. If pressed, I would at this point probably agree with the academics who first and foremost define the bare term "service" as an act.
One peculiarity I am still thinking about is whether the offering sets expectation for the outcome or the act. I think it is both, but they are different expectations.