John;

I don't have access to all of his proclamations so I can't check that.

The perigee shift only happens if syzygy is 2 or 3 days before the quake and perigee is also within 3 days before so dropping off the end doesn't happen.

I'm thinking this is related more to the number of tries. Given there are 26 syzygies per year (more or less) and only one great quake (usually) perhaps the odds are greater than the simple time covered by windows.

Roger