Maybe I'm way off on this, but didn't Meagan say "You've been on leave for a year, and you didn't come to see me?" Don ran into his replacement on the way out of the door whenever he was put on leave. To me, that means, when Don was let go (over a year ago according to Meagan), he ran into Lou, = Lou has been there a year.
i just assumed that those things lined up. My timing on this show is thrown off completely, honestly.
It's only been a couple of months. Don got cut loose in November/December of 68, and the show picks up in February of 69. Megan makes it seem longer because she says "You got fired last year"