There appears to be some leeway in the interpretation of an acceptance tick mark.

Best answer:

The tooltip of an accepted answer states: "The question owner accepted this as the best answer...".

About - Stack Overflow states that "The best answers show up first so that they are always easy to find." And since accepted answers show up first (regardless of the vote count), one would tie Accepted=Best.

Most of the statements that I have seen support the concept “Accepted=Best” (as a nice example, this accepted answer), and leave the “It worked” concept for the upvote.

Good answer:

About - Stack Overflow states that "Accepting doesn't mean it's the best answer, it just means that it worked for the person who asked" (which would formally imply that the system should allow for multiple tick marks, but this is a separate discussion).

Is there an official position on this?

There are some related posts, but I did not find in there the answer to my question.