“The artist formerly known as John Smith.”
I’ve never heard or read “late” used to designate a name or title change.
Garner’s Modern American Usage suggest that using “late” more than five or so years after a person died “is going to strike most readers as odd… Of course, there is no absolute statute of limitations; the question is whether a fair number of reasonable readers would know or need to be reminded that the person has recently died.”
The same source says you can use it to pay extra respect or sorrow to someone (e.g. the late Lady Diana in the weeks after her death), or to indicate in historical contexts that someone had only recently died at the time being discussed. So, “the late John F. Kennedy” generally sounds weird now but “Congress passed the Civil Rights Act of 1964 as a tribute to the late John F. Kennedy” seems reasonable.
I think the “late John McCain” is important in recent news coverage. First, McCain didn’t die that long ago and saying “late” helps to catch everyone up on the news. Second, and probably more importantly right now, McCain is in the news because the Trump is criticizing him. It’s worth jolting readers with the realization that Trump is shamelessly deflecting attention from his own misdeeds by attacking a dead hero.
I think the term “late” is also used when there may be confusion as to the person to whom you are referring. (That is, of course, if only one of the possibilities is dead.) So you might say, “My sister once met the late Barbara Bush” in order to specify that you mean the former First Lady.
“Yes you do. The rule is that he’s “late” if a great many people still remember him being alive. And plenty of us remember JFK.”
Here’s a cite discussing in some detail how there is no fixed rule, quoting conflicted advice
Though including "Dictionary of English Usage says other have suggested anywhere from 10 years to half a century, though “our evidence shows that the late can be applied to people whose lives were recent enough to exist at any point within living memory of the writer or speaker.” "
It goes on to advise thinking through usages which might come out oddly, like ‘the late president was preoccupied with X’… but he wasn’t dead back when he was preoccupied.
The article also mentions a 5 yr rule from one style source and 10-50 from another. Seems to me it’s typically something like 5 or 10 for well known public figures, perhaps you can get away with more in cases where you can’t take it for granted the reader knows the person is dead, and you don’t want spend extra words explaining ‘the early 20th century philosopher’ etc.
On the case you responded to, I could see as a rhetorical device referring to ‘the late’ JFK addressing an audience of elderly pro-JFK people, to communicate the speaker’s understanding of their point of view, his death still vivid and perhaps hurtful, not as long ago to them. Which like most rhetoric you could call corny or manipulative I guess if you want to be negative about it, and depends on the degree. But I agree it’s very unlikely you’d see a major news outlet article now or any time recently referring to ‘the late’ JFK.
Also I assume varies by language and culture for other languages which have that device. AFAIK ‘feu’ in French is equivalent but can also refer to a thing which no longer exists, and I’m not sure if it’s as common. In Korean 故 (which you usually write that way, the Chinese character instead of or in addition to the Korean alphabet phoneme “고”) seems to be used more permanently than ‘the late’ in US English. News articles of recent years have still used it before the name of the first ROK president Syngman Rhee (aka Yi Seung-man) who died in 1960, at least the first time the name is mentioned.
I’m open to correction on this. And I admit that even by my definition, JFK would no longer be “late”.