It is curious that the wiki mentions Voyager I data for some claims and we use those to verify Voyager I data?
2) When your experiment yields results that match your hypothesis, you consider that evidence.
3) When you have sufficient evidence, you upgrade your hypothesis to a theorem.
According to the Wikipedia article, we've got at least two probes that are producing results in line with our hypotheses. The bar for wikipedia is "sourced", not proven theorem with scientific rigor. In this case, we're in some nebulous area between 2 and 3. I think that meets the bar for an encyclopedia, which is intended to serve as a summary for these types of things.
Hit the sources and the transitive closure of references for more details.
A theorem is a mathematical result: something proved logically from (possibly physical) assumptions.
To my mind, in this context, the difference between maths and physics is that maths is exhaustive while in physics we don't usually have exhaustive evidence so we have to work with what we've got.
I'm less certain than I was before I read your post, though - so I stand to be corrected :-)