We can't quite call it a rule yet, but that's three second Wednesdays of the month in a row.
http://www.nintendoworldreport.com/news/49074/december-nes-games-for-nintendo-switch-online-releasing-on-12th
Patch Tuesday will now be followed by NES Wednesday.
The December additions to the NES subscription service - Wario's Woods, KoeiTecmo's Ninja Gaiden, and HAL's The Adventures of Lolo - have been tabbed for release next Wednesday, December 12. As with previous releases, this will likely be early in the morning in North America.
December's games are the last of the three months revealed prior to Nintendo Switch Online's launch: according to the Nintendo website, the games will be revealed "once they’ve been selected". Also not revealed is which game(s), if any, will receive the "SP" version that offers a head start on the game.