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I assume you are talking about 3 accounts with negatives that fell off. How bad were the negatives (e.g. 30 day 60 day, bk)? If they were "only" 30 or 60 day lates they were not effecting your score to any significant amount anymore. Other possible reasons are other changes in your reports: decreases utilization or increase in AAoA for example.
This all assumes that we are talking about actual Fico scores and not fakos.
ETA: Hauling is obviously a much faster typer than I