This continuity guideline is hilarious, although if I were the Mutant Enemy writers I'd be choking back the urge to throttle the smug little shit who wrote it :-). The best parts aren't the advice, but are the cheat sheets for characters.
And from the "ok, even I am scared now" department comes this timeline. Like all fiction, I squint and let each Buffy episode wash over me. It never occurs to me to find inconsistencies or to draw up timelines. In fact, I quail at the thought of how much time it would take to draw up this kind of chart.
--Nat