My general observation is that you dont want to change your vegetative nutrient ratios until after week 3 of flowering
You don't see this reiterated too much.
I've always kept up my high N nutes through flower, just with gradually less frequency as they reach the finish line.
IME, Grow and Bloom formulas both have what it takes to carry a plant to harvest, just not optimally. And it seems the optimal mix is for some reason not solely found in one formula *cough*.. $$$... *cough*