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Any simulator is going to be inaccurate. They cannot take multiple changes into account, and also, if they were accurate at predicting what happens in various situations, we'd know everything on inner workings of that particular scoring system.
In general, reducing utilization when thresholds are crossed causes some points gain. How much tends to be profile dependent.
If you feel inclined to do so, you can list all your cards with limits and balances.
That may give others some idea at what kind of gain you're looking at, if any.
Credit score simulators are just a thing that credit websites hack together real quick so that they can add it to the list of things that they offer. That's their only purpose. They serve no purpose whatsoever in actually simulating your credit.
Even MyFICO, which is the website made by the very people (and only people) who know EXACTLY what the scoring formulas are, don't get the simulations right. I suspect in that case, it's not due to laziness but rather due to intentional errors to keep people from playing with the simulator parameters and figuring out the formulas. Remember, FICO is a company whose sole source of revenue is their exclusive formulas, so their future depends on them keeping people from figuring out exactly what makes their score what it is.
Every other website is really just winging it with absolutely no idea what would cause your scores to change and by how much, because they don't have the faintest idea how your scores are calculated. They pretty much just say "Yeah paying all your bills on time for 24 months will probably boost your score by 30 points, sure. Sounds plausible, so there you go."