In a few minutes, I'll get back to work. But first...
So I only just learned today that -- like "The Star-Spangled Banner" -- "Hatikvah" is also a combination of a pre-existing poem and an unrelated old tune. Now, admittedly, the Star-Spangled Banner just directly copies both its sources, whereas Hatikvah modifies things a bit more. (The tune is a big difference if you compare directly to "La Mantovana"; less so if you compare to "Carul cu boi".)
Still, it struck me as an interesting coincidence. Is this a common thing among national anthems? I mean, I could easily believe that adapting them from preexisting poems is, but also using unrelated existing melodies? That would be a bit more surprising.
Well, if I had the time, I'd start going down Wikipedia's list of national anthems and counting. But I don't right now, so I'm just going to note this coincidence as one to follow up on later. Or let someone else count.