Thank you in advance,
As far as the year 1800 concers, is it wrong if I say one thousand eight hundreds???
Not wrong, just different, as in not all that common or modern, and there wouldn't be an -s on hundred.
This Constitution shall take effect on the first day of January, in the year one thousand eight hundred and seventy-four, for all purposes not otherwise ...
WILLIAM THE FOURTH succeeded George the Fourth, in the year one thousand eight hundred and thirty, and reigned seven years. QUEEN VICTORIA, his niece, ...