The diff soil may explain why plants exhibiting a difference.
The plant in the middle is the most Nitrogen deficient. When the buds fan leaves start yellowing than there will be trouble b/c the new buds will not have enough N to grow.
The one on the left although is green, is already turning N deficient on the lower leaves at what I first thought would be a MG deficiency but is not. I would give her those nutes you have full strength every feeding and dwindle down to ¼ strength when you get to be about 2.5 weeks out. There is a low enough N in those ratios that it will not delay her from flowering but also stop her from eating her own.
The right one should get full nutes for next 2 waterings and than ¾ for 2 than ½ for 2 and than ¼ for 2. The middle one will need full strength all the way through with the addition of Nitrogen I believe at this stage of the game. They will be relying on your Nitrogen feedings to continue to blossom. Normally that N-P-K ratio you have is fine for flowering, prefferely higher with the K, but in your deficiency you may need more N. I would stop by your hydro store and ask them if they carry a 6 N, 5-10 for P, and 5-10 for K. That would work much better. The 2% N may not be enough and you dont want to blast them just to get her N up. More like a Veg nute mix. You could also feed with what you have at full strength and pick up a N specifically nute like a Vita grow. Keep in mind you will only be using this for a couple weeks.
Here are some more:- I think in addition to the quicker acting bio buzz that an organic slower acting will def help. Like using an organic and chemical source:
Chemical Nutrients
Vita Grow (4-0-0),
GH Maxi grow (10-5-14)
GH floraNova grow (7-4-10),
Dyna gro Grow (7-9-5)
Organic Nutrients
Dr. Hornby's Iguana Juice Grow (3-1-3)
Blood Meal(12-0-0)
Fish Emulsion (5-1-1)
Seabird Guano (11-13-3)
Crab Shells(2.5-3.0-.5)
Marine Cuisine (10-7-7)
Mexican Bat Guano (10-2-0)
Age old Grow (12-6-6)
METANATURALS Organic grow (3-3-3)
METANATURALS Organic nitrogen (16-0-0)
Too little nitrogen too early in flowering with premature yellowing WILL result in slowing of bud growth leading to decreased yield.
Im sure the plant knows what her own Nitrogen levels are and what type of bud she can produce with that in mind. Basically she is doing what she is supposed to which is taking the Nitrogen from those leaves-that is their purpose. But that new growth on the middle plant looks yellow which means you will need to act here asap. Those leaves will never regain color but the goal is to get them to stop yellowing any further and for all new growth to be normal and green. When she is ready, than she can be let loose and she can suck all the N she wants out of herself. Three weeks in flowering should have more green growth than you have now.