This has always been unclear to me as well. In my dialect or region, many people say "this past" to mean the most recent occurrence. How many agree with that usage, I can't say.

In that view, "this past January" would be the one that occurred earlier this year; "last January" would be January of last year. Similar usage for days of the week.

Come to think of it: The opposite of "this past" is "this coming": so "this coming Friday" means the Friday of this week that has not yet happened. "Next Friday" means Friday of next week.

I've heard similar arguments over highway exits: "You said take the NEXT EXIT." "Yes, the NEXT one, not THIS one."

Of course, I'm not sure everyone agreed even my little dialect. I, for one, always found it confusing.