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Write a goodwill letter to your loan providers, tell them your situation. Maybe you have foreberance left, maybe there are other options, or if nothing else maybe the goodwill letter will work by itself. Give that a try, getting just a few of those lates knocked off will really help you.
Rehab is only for loans that are currently in default. Foreberance is for when you cannot currently make payments, and yes, they will retro it, but not 3 years back! Student loan lates are almost impossible to remove--but some have been successful. I think you would be better served by getting a third credit card--Fico likes at least 3 lines showing, with only one reporting a balance under 10% each month. SL lates from 3-4 years ago will not keep you from getting a mortgage, but if you can knock out some of the higher interest loans, you will have a better DTI when you apply.