that's how it works right now, in fact right now it's worse, if you were at say 450/500 it'll give you title for camping 500 nights without the variable itself, so you're still at 450 out of whatever the next title is, so the reward is effectively 0 days
But that's not how it works IIRC. Once you hit 500 in your example you'll still gain a level from normal progression.
Let's say there are these variables, gonna use goober numbers just for illustrative purposes:
TitleLevel = 2;
TitleCurrentTargetIndex = 2;
TitleProgress = 350
TitleProgressTarget = [100, 200, 400, 800, 1600]
So your title is currently level 2 (because you hit the 200 Progress target, and every time you hit a progress target, TitleCurrentTargetIndex goes up, so it was first at index 0(100), then 1 (200), then 2(400).
Now let's say you get a dungeon reward +1 level on this title.
TitleLevel goes up, but TitleCurrentTargetIndex doesn't and it's now:
TitleLevel = 3;
TitleCurrentTargetIndex = 2;
TitleProgress = 350
TitleProgressTarget = [100, 200, 400, 800, 1600]
Next you hit progress 400, TitleLevel and TitleCurrentTargetIndex go up by 1.
TitleLevel = 4;
TitleCurrentTargetIndex = 3;
TitleProgress = 400
TitleProgressTarget = [100, 200, 400, 800, 1600]
Since all titles have a universal cap of 10, this benefit carries on until that cap is reached.
It's been a while since I grinded but I could've sworn that's how it works.