Although I still find the perfect tenses correct, it seems I have to take back what I said about "since" requiring a perfect tense. See this example I found here:
- It was the band’s first live performance since May 1990.
That would account for those native speakers finding the past simple to be the best choice.
The example on the Cambridge Dictionary seems to illustrate a different case. I suspect that the "since May 1990" actually modifies "the band's first live performance" rather than the verb phrase beginning with "was..."
This type of since-phrase most commonly occurs with superlative adjectives or ordinal numbers. If the nominal phrase along with the since-phrase functions as a subject, we may see more clearly that it has no relation to the main-clause verb "was."
The band's first album since 2008 is going to be released next month.
So, it seems to me that the CNN sentence cannot be explained in the same way.
Concerning your other examples on that other forum, I agree that, for your sentences to be correct, you should have used "be married" (an ongoing state, not a one-time event):
Joe met Sarah in 1997. They have been married since then. (Assuming they are still alive and married.)
Joe met Sarah in 1859. They had been married since then. (Assuming they are no longer alive.)
I have no problem with your revisions. In my thread on the other forum, I intended to compare the ungrammatical "Joe met Sarah in 1997. They have married since then" with the grammatical "We were divorced two years ago and she has since remarried."
Both have an instance of "since," but only the latter is compatible with the present perfect. That is what's puzzling me.