....3 SN / per century is possibly only an "average".

A good example of "averages" is that from coin tosses.
30 coin tosses = [average] 15 heads; 15 tails.
But try this experiment yourself.
Make 30 coin-tosses.
Break the 30 coin-tosses into five parts.
(1) First part: 6 heads; 0 tails.
(2) Second part: 3 heads; 3 tails.
(3) Third part: 0 heads; 6 tails.
(4) Fourth part: 0 heads; 6 tails.
(5) Fifth part; 6 heads; 0 tails.
--------------------------------
Total: 30 coins tossed = 15 heads; 15 tails.

Of course, all coin-tosses don't work out that way, but they average out over the long term.

So...IF the 17th century was typical, then there are an "average" of 2-3 SN / per century
in this galaxy. But like the divided "parts" of a 30 coin-toss, the centuries since then have zero SN on one side of the ledger.....That can quickly change to BALANCE things out; to restore
the AVERAGE....It may mean perhaps 4-5-6-7-WOW-TERRIFYING numbers of SN / per century
in years and centuries to come to restore the AVERAGE.

Jacob

Voila! Apres tojour, vu comprend l'cosmos?