Not once per 823 years, once every few years

Have you received this email yet?

This October is very special. It has 5 Fridays, 5 Saturdays and 5 Sundays, all in 1 month. This happens once in 823 years.

Well, no.

My daughter was born on Oct. 31 (Halloween babies are special!) in 1993. Whenever Oct. 31 is on a Sunday, Oct. 1 must fall on a Friday, and so will be followed by four more Fridays (8, 15, 22, 29), hence five Saturdays, too. It happened in 2004 and will happen again in 2021.