@BioMed As far as I know there are somethings which are known to your DSO, and something not known. They know how much courses you had taken each sem, whether you maintained full time course requirements or not. How much you might have worked on campus. They will make decisions based on whether you enrolled full time or not when it comes validating your i-20. There are students who work more than 20 hr per week on f1 and still have valid i-20, you know that. Gas stations, convenient etc.

Now, to your question that can you legally work more than 20 hrs per week? Now read this, what if you worked for only an hour per week offcampus,, forget about 20 hrs, did you violate f1 conditions, since f1 is allowed only to work 20 hrs per week ONCAMPUS, only economic hardship category is allowed to work offcampus. So, i think the "20hr" rule is a just a mere satisfaction, since we are used to it. I guess you would be allowed to work more than 20 hrs, and you should take full time courses at the sametime. Talk to your DSO, and let us know what they say.