The "General Directs are only in the first half of the month" rule has been true for 7 years though.I wonder if this rule still holds?
There was also a "General Direct within 14 days of a Pokémon Direct" rule that's broken now.
20th and 27th are still possible options. It's quite possible Nintendo wanted to do the AC direct prior to doing a general (probably makes more sense that way from a marketing perspective).
It's clearly intentional by Nintendo and not just a pattern.