not a huge deal IMO....every time I crack new seeds some end up growing more than one main shoot. As long as it is healthy, enjoy watching them grow, and if they are to be mommas, remember the tops dont clone as well so more than one shoot can be good and would give you more from the bottom to...
I have yet to try any 12/12 form seed, but I use clones. Any time you make a plant do something it wasnt intended to do it is bound to have little odd things go on. I wouldnt fret over one yellow leave. Sounds like you are feeding it planty. Check for root bound though. growing that fast the tep...
Just dont overdue it...better to not nute burn it (seems to be a popular term around here) remember any changes you make will take 7 days or so to show up, dont over mother her ;)