Alright let me break it down, really think I should just make a TL:DR for this since I have to explain it every time I bring the in-game site up (nothing on you, I'll admit it is bewildering if you have no idea what it is).
This
https://www-aaaba-lp1-hac.cdn.nintendo.net/en-US/index.html
Is the site Smash Ultimate opens in-game with all the announcements, Spirit Events, and what not. (I know the link looks weird, trust me it's fine.) Opening the site on an Internet Browser let's you see that each post image is actually numbered in it's filename, they are catagorized based on the type of message they are (tournament, Spirit Event, and everything else) and numbered in more or less sequential order, so when the numbers go blatantly out of order, like say the general posts jumping from 103 to 110, it's clear something is up.
In the case of a massive jump in general posts, it means the posts meant to come with a major update are in the system and we can pretty easily figure out what they are because they do the exact same posts with every character. A warning about the update coming soon, the Version Update itself being released, a post about the Challenger Pack, and a post about the Fighters Pass overall. Just plug the numbers in, and the rest of the posts are for the Mii Costumes. Worked perfectly when we did the same thing for Steve, see no reason why it wouldn't here.