The numbers of your sentinels should be correct, I believe none of the others are.
I don’t think it’s quite that simple, eg I think if a guild did 0 points when they were in Bracket 1, I don’t think they would drop to the bottom possible bracket the following week (though they would fall a long way) But I do agree they look at your points compared to guilds over a large number of brackets, rather than just the ones above and below you.