more like 700 years worth, with most of it the last 500 (13-18th century), so yeah, shit bound to hit the fan until sterility is the common defect over such time spans. You can prob get away with it for a few generations (has happened before with the Toba eruption 74,000 years ago, when all but 10-20k pairs of humans were wiped out worldwide, so it was either breed your family/close village relatives or go extinct and that volcanic winter lasted nearly 100 years/5-6 generations) but odds are shit after 5 or so and nearly 0% after 25+ like the Hapsburgs. At least they mostly stuck to breeding their cousins for the most part, otherwise they would have probably died out even sooner. Modern day Pakistan currently has the same problem times a million, as apparently the incest fetish is far more common there with 61-65% inbreeding (ie 6 out of every 10 marriages/births are to cousin or closer parents, and people give Alabama grief). That seems to be a common theme among Islamic countries, maybe due to arranged marriages and the females get no say in it, as in most of them it's over 45% so probably the next major religion to die out in the next few centuries if they follow the Hapsburgs.