> a previous occultation of Leona in September 2023
Seems contradictory. Do they mean rare for any given star?
> An occultation of a 1st-magnitude star is rare — such an event is visible from Earth only every few decades
and
> That changed on September 13, 2023: In advance of the December event, Leona occulted another object, this time of a 12th-magnitude star.
It makes sense: there are only a few bright (1st-magnitude) stars so occultation of them is rare, while there are a lot of stars in the sky so occultation of some (dim) star is not very rare.
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Edit: We can come up with a more explicit expression. If each individual star has an occultation once every k days, then "at least one of N stars" has an occultation roughly once every 1/(1-(1-1/k)^N) ≈ k/N days. So if with N=22 (the number of 1st-magnitude stars: https://en.wikipedia.org/w/index.php?title=First-magnitude_s... ) this is once in 40 years (say), then with N = 10000 stars you'd see about once a month.
Having it happen to a star you're actually aware of and can see tonight is pretty cool