Factoids (urban legends, myths, misconceptions ...) are associated with as famous actual phenomena (people, places, events ...) as possible.
This law has been put forward in different contexts with different wordings. But if it's ever been given this general form before, I haven't seen it.
It is particularly strong when it comes to people. Let's start with those examples. Like the most obvious genre of them all: Quotes.
Because it is a well known fact that memorable quotes coined by unknown, less well known or anonymous people sooner or later are attributed to famous historical people. The supposed source have to "fit" the quote in question (blunt humour = Churchill, sharp witticisms = Mark Twain, clever deep humour = Einstein etc), and the more well known the better. Such examples are produced daily, in vast quantities.
Or take ghosts. Here, a ghost researcher describes a house which is said to be haunted by Frank Sinatra:
However, as none of these alleged manifestations can be demonstrably linked with the actual presence of Sinatra, I rather think this is an example of what I term 'Brighton Pavilion Syndrome', the process where any vague ghostly manifestation or report of a sighting is at once linked with the most historic personage know to have frequented a building in its past.- Alan Murdie, Fortean Times 330 (August 2015), p 19
An American president in a positive context is, depending on century, Washington, Lincoln or Kennedy, preferrably. A European queen is Marie Antoinette. An episode regarding a WW2 general is, depending on country, generally attributed to Rommel, Montgomery or Patton. Every country has its preferred historical celebrities of various kinds.
I first considered a law on famous people. But even if they are the most common, there are many other kinds of examples of how factoids attempt to be associated with the most well known instance in the given field.
If an episode deals with a war not too long ago, World War II is the preferred one. (If it's located to WWI, you're probably in the UK.) In USA the Vietnam War is far more prominent than the Korean War.
A myth on fast food will, if it gets big enough, probably be about McDonald's, sooner or later. A myth on a soft drink will probably be about Coca-Cola, sooner or later. Those brands are not only known everywhere (a myth about French Orangina, Italian Chinotto or Swedish Julmust would have to be adjusted before going global), but they are also better for myths, somehow, than Burger King and Pepsi.
Sometimes the rates change. A rumour about a secret elite society would a few years ago have been about the Free Masons; today, the Illuminati is the cool one. Failed nuclear power? Today Fukushima, before that Chernobyl (and before that Harrisburg, I assume). Tall tales being told 50, 100 or 150 years ago could have been about people, events and phenomena few know about today; if those tales are still being told, such components have been adjusted for our time. And the more well known components, the better. (That's one reason why rumours and myths are so valuable as history, even when they are patently false; they can tell us something about the people who believed in them.)
There are certainly exceptions from the factoid law of attraction, everywhere, all the time. But the tendency is clear enough: Factoids are, in general, associated with as famous actual phenomena as possible.