Do Syrian rebel groups ever have to substantiate their claims?

"“During the last three days, we have been hit by over 120 barrel bombs,” said Ahmed Abu Talal, a rebel belonging to the Islamic Front group".  Is there any claim that they make get verified? If they were to say that nuclear weapons were dropped on them (and I believe that one rebel group made that claim every in the war), would that get verified or printed as is?  I mean, it could be 5000 barrels but how was the number reached?