PH not a problem I think. It is most likely nutrient. When you are holding plants for replacement and not wanting them to grow out of their container... you can "bonzai" them sorta by withholding nutrients and they will remain a managable small size. Then when transplanting them as a replacement they will take off like crazy once nitrogen is applied and are no worse for wear and tear.
A good example ismy present grow which were planted from small cups after their brothers from same planting were already in the kiln.
You know what, let me ask you.
My Burleys are the only ones that look stunted. My current Burleys that are in their own SOLO cups are about the same size as the ones in my Skoal seedling tray. The only difference is that they aren't yellow. They have been outside for at least a month. Like everyone says, once transplanted they will take off, has not happened yet with me. I will say, I have grown from seedlings in doors, and once place outside they were growing almost an 1/2" a day.
My Samsun and Havana took off in the seedling tray and my Virginia started slow. Now all but my Burleys are taking off. Yet, they are not taking off like others have mentioned.
I guess the only thing that I can say about all this is, "if they are doing ok, don't bother them".