My account notes on the reports vary some from CRA to CRA, but I legally settled for less than full amount. The changes to my scores happend in steps as I paid them off. It took them a couple of months to get them all annotated correctly because I had to deal with two separate firms (one of them a lawyer's office), and the datafiles weren't correct the first time. But, when they updated the amounts to $0 balance, they reapplied the CO note that made the fico react as though I just missed a payment. It wasn't until I disputed this and they removed it before I made the full recovery - about 40 points. It's hard to say how much that particular payoff affected since it occurred over a couple of months and there was aging of the baddies happening as well.
In my case the score jump was entirely based on improvements to my credit utilization percentage. I've no evidence whether having settled for less than full amount has any affect on my score. Now, they are between 659 and 673, so I don't mind so much.