I thought JJ was 3 part. I'm not sure if your reference to parts a and b mean you have two of JJ's 3 parts, or it's something else. I'm not familiar with Agrogreen, what it's NPK is.
If I were you, I would use the 20-20-20 at half the label's recommended strength. If it says 1 tsp per gallon of water, use 1/2 tsp. That's a common starting point when using something others haven't tried yet. (Have you mentioned the brand of the 20-20-20?).
You don't need a lot of stuff. You don't need to increase PK in flower. If you do need to, your plants will tell you (purple leaves, for example.).
There is no step-by-step recipe for growing. If you try to follow one, you're still going to run into deficiencies from overfeeding, underfeeding or imbalanced NPK. Whatever you do won't be perfect and you'll still have to learn how interpret the condition of your plant. So, you might as well keep it simple with the 20-20-20 (assuming it's a decent product, we don't know the name of it yet), and spend time at growweedeasy studying the photos of deficiencies (you'll want to focus on N, P, K, mg and ca).
After you get through one grow you'll have more confidence in preemptive strategies (like, knowing that you need to add epsom salt in early flower to fight mg def. Or, blending in some higher PK fertilizer in late flower. But, by comparison to growing 20-20-20 all the way through (and having a stable baseline to assess your plant's response), the difference in growth will be minimal. If you get all science-guy about it, mixing a lot of stuff, the risk is that you won't know what caused it to go wrong. Chances are it will go wrong. Might as well keep it simple so you won't have as many variables to adjust.
I know it sounds complicated. But, after 2-3 grows you'll feel like an expert. So, just accept that the first 1-2 grows will be like shooting in the dark. Keep it simple. Your goal should be to learn as much as you can from the grow, not have a perfect grow.