On the other hand, one may also argue if Brett did something he knew might have repercussions he wouldn't have kept a 1982 calendar, would he?
It's arguable that a lot of things(that have repercussions for ordinary non-connected folks) that this guy did were devoid of repercussions given his white(and other) privilege which he shamelessly flaunts.
That aside, all this calendar does is
(1) proves he is not telling the truth about drinking on weekdays,.
(2) proves that Dr. Ford is not making up implausible stories.
(3) proves that their social circles did indeed cross(she was going with Squi I believe).
(4) provides a corroborating time frame for such a party within the period she alleges this event took place.
It does not prove that he attempted to rape her. But it shows he is at
best economical with the truth. It becomes more apparent when you factor in his evasive answers and downright stubborn refusal to support an FBI investigation that could theoretically clear him.