So... which date? Do you mean the third Friday in december (12/21)?
Sooner than the dates you mentioned in above quote.
The tourney-legal date, and the answer to your question, depends on whether certain criteria is met involving when they were released.
Tourney-legal dates used to be three weeks after release, until Sun & Moon's release, when they made the tourney-legal date of new cards either:
1. the first Friday on the month after the release of card in question(in case the product was released on the week of the third Friday--or anytime on or before the fourth Friday of release month. Examples of Pokemon TCG products released on the first Friday after release month include Snorlax-GX, the upcoming Zekrom-GX, among other promos released within the period between the day after the second Friday of release month and the fourth Friday of release month), or...
2. the third Friday of release month(in case the product was released on the week of the first Friday--or anytime on or before the second Friday of release month. Examples of Pokemon TCG products released on the third Friday of release month include cards within present-day and future main sets(always released on the first Friday of release month), the new weakness-nullifier Solgaleo-GX, among other promos released within the period between the day after the fourth Friday of release month if released before the month rolls over or the month before release if released after said rollover, and the second Friday of month released).
In this case, Lost Thunder will be released on November 2nd, the first Friday of release month, so the third Friday of release month, November 16th, will be that expansion's tourney-legal date.
