The Caption This! and Complete This Phrase / Fill In The Blank(s) boards are divided by years (hence Caption This! - Year 1, Complete This Phrase / Fill In The Blank(s) - Year 2, etc.). DS debuted on June 27th, 1966, so year #1 goes from June 27, 1966 (Ep #1) through June 26th, 1967 (Ep #261), and year #2 goes from June 27, 1967 (Ep #262) through June 26, 1968 (Ep #522), and so forth.
And so far as days off go, with the exception of rare occasions like the NABET Strike and when they converted over to color cameras, the only weekdays when DS didn't tape was on holidays like Thanksgiving and Christmas.