I think perhaps you’re confusing “Unknown” with “Unsupported”.
The people at MDN have apparently not gone back to these pages to determine their status or when the browsers adopted the ability. caniuse apparently has.
They’re both equally authoritative; they source updates through an open Github fork-and-merge process, with a review process as part of the merge.
caniuse is a specialized site for compatibility, MDN is more concerned about the specification and Mozilla’s explanation/implementation of it.
It should be pointed out that Mozilla is not the creator of the spec themselves, they are a member of the W3C group, and so contribute to it, but they do not themselves define it.
Ok, GitHubis o ver my head, but I’ll take it that if CanIUse says stroke-dasharray is supported by browsers then I can spend time learning more about it in an effort to learn how to make pie charts using SVG.