I recently opened a dispute with TransUnion because a collection account (1 of 2) had been listed twice. I don't know how I never noticed after all this time, but whatever. Transunion came back and said it was a duplicate account and deleted it right away. My credit score only went up 1 point and I now only have 2 accounts in collections.
I can't tell you how many points yours will go up, but I believe it depends on how old the accounts are. For me, the account will drop off my credit report by the end of this year, so it's pretty old. I guess one point is that much closer to my goal, though, right?
FICO scoring places a consumer into a scoring category, or "scorecard," prior to scoring, with scorecards varying in their scoring based on comparison of consumers who meet some overall criteria. They are also called scoring "buckets."
For payment history scoring, you remain under a less-favorable scorecard if you have remaining major derogs.
Thus, the scoring impact upon removal of one major derog, such as a collection, public record, 90+ late, or charge-off, depends as much upon what derogs remain as upon the removal of the derog.
Significant score increases are usually not obtained until the collection is the last major derog, and thus you are moved to a "clean" scorecard.