Yes it still need N in flower and it will be given in the right dosage if you give them bloomnutes. Now if we say there is a shortage of N the usual bloomratio isnt enough to compensate. like i stated: u dont really wanna compensate all the needed N because the plant likes to make flowers anyway so take the yellow leafs a bit as a loss and try to up the N for a few days/1 week and after that use the usual bloom npk ratios.