Hi GT
You quoted Roy Reinhold as saying:  "...There are 5 leap centuries in that
time frame (400, 800, 1200, 1600, & 2000 AD). All of the other century
years
are not leap years even though they are divisible evenly by 4, this is the
crux of the changeover from the Julian to the Gregorian calendar..".

I'm not an expert, but as I understand it, the Gregorian calendar kicked in
on October 4th, 1582.  October 4th was followed the next day by October
15th.   This correction was to compensate for the ever growing drift, from
having one too many leap years every century.  Up until that time, EVERY 4th
year was a leap year (starting in the year 8 - the year 4 was not).
Centuries included.  So the year 100 WAS a leap year, as was 200, 300 etc.,
up to and including the year 1500.  It was only after the October 1582
correction that the additional rule of century years divisible by 4 were
leap years was implemented.  1600 WAS divisible by 4 so it WAS a leap year.

Ultimately, I don't think that this contradicts his date by more than 4 or 5
days.

This is how I've counted it (please correct me if you find an error) :

Century # of days Reason:
1-99  36158.........no year zero & year 4 not leap year (due to an
earlier correction attempt)
100-199 36525
200-299 36525
300-399 36525
400-499 36525
500-599 36525
600-699 36525
700-799 36525
800-899 36525
900-999 36525
1000-1099 36525
1100-1199 36525
1200-1299 36525
1300-1399 36525
1400-1499 36525
1500-1599 36515.........10 day correction
1600-1699 36525
1700-1799 36524.........1700 not a leap year
1800-1899 36524.........1800 not a leap year
1900-1999 36524.........1900 not a leap year

Best regards,
Keith