It's terribly hard to work out the "reward" some times. I suspect you might have missed what your eldest was treating as a reward for the paddys. It could be something like leaving the shop before finishing what you went there for, as they didn't like that shop for some reason.
I think the keys are not to give in once you have said no(*) and if you make a threat be prepared to carry that threat out. So don't make threats you can't carry out! It only takes one or two threats not to be carried out for the child to come to the conclusion that threats are harmless and can be sfely ignored.
(*) At least not as a direct result of throwing a paddy or other unacceptable behaviour. Tell them that if they calm down behave nicely for a pewriod of time they might (don't tell them the will or promise they will) get what they want or some other reward.