Hello,

As you have mentioned that your son got a self financing college in the 2nd allottment and he joined it and in his 3rd allotment he again got that same college...
Let me tell you that there is nothing to worry in this case... The seats allotment of previous rounds doesn't matters for the mop up round.. So, YES!!!! He is eligible to participate in the mop up round... See, the mop round is to fill the vacant seats for different NITs, IIITs and GFITs and its cutoff goes somewhat higher (rank wise). So, everyone who have qualified their exam are eligible to participate in the mop up round to get seats for them.. And the candidates with high rank also have good chances of getting seat in these round...

Wish him all the best!!!

I hope this would help you. For further queries please feel free to write me down in the comment box.