I have heard that international students should not apply in r3 as there are visa issues and very few number of seats are available after r2. Is that true, if an international is not able to apply in r2 should he wait for next year or give it a try in r3? ANy idea??
It is definitely hard to get in by applying in R3. Well, I should say by applying in the school's last round (Cornell and UNC both have 4 rounds, so the 4th is the hard one there.) Unless you're some sort of amazing, world-renowned genius, apply as early as possible. Particularly to the top schools. Also, there usually is no scholarship money available in R3.
Some schools don't allow internationals to apply in R3, because of the visa issues. Even if you could apply that late, with bureaucracy the way it is, you're definitely taking a gamble.
But let's assume the visa would be ok. Some people say that schools don't like reapplicants, so if you apply in R3 and don't get in, you'd have a hard time the following year. You may want to choose a whole new set of schools. I don't have any hard data on it, and it may very well vary by the school, but being a reapplicant is probably not the most desirable circumstance.