I personally waited for the new tradelines to appear on my report (bought by Sallie Mae right after I completed my rehab). Then I started disputing. And I disputed as often as I could. I know there is wording floating around the forums on what to say when you do dispute - I just said something along the lines of "student loan successfully rehabbed - collector agreed to removed negative remarks from credit report". Experian and Equifax happened pretty quickly - it only took me three or four disputes. Transunion took almost four years. However this is definitely a YMMV thing because I've seen anything ranging from they removed themselves before dispute, to people have not gotten them removed.
Have your loans been picked up by a servicer??
in the garden until 2019!
Technically you could dispute now. I don’t see a problem with doing it before your new tradelines report. That being said, you could also wait it out to see if the new tradelines shownup free and clear of any late remarks. You could be one of the lucky ones. On my credit report, my old tradelines were a mess while in limbo between getting picked up by my new servicer. Once they did get picked up, they became nice and tidy and easy for me to dispute what needed to be disputed.