I'm misunderstanding something... did you add 2 week old chicks?
The difference between layer and grower (or ANY other confusing term on the label) is protein and calcium levels, MAINLY.
Too little protein in still growing birds can delay their development. Too much calcium, fed long term to non laying birds *can* (doesn't mean will) cause gout or kidney failure.
I personally never feed layer as it's usual 16% protein is the bare minimum for light bodies layers like leghorn, while dual purpose breed like Wyandotte, Orpington, Rock, Marans, Reds, and other will do best with about 18% protein.
Since I always have different ages and genders in my flock including molting and brooding hens and chicks... I ALWAYS feed Purina Flock Raiser with 20% protein and 1% ish calcium... and provide oyster shell free choice for active layers on the side.
Some people will put a 12 week old pullet on the layer... and may never see or notice health issues... It wouldn't be my choice. Instead I would choose to put all layer on the higher protein feed... feathers are made from 90% protein and it's amino acids... And most birds will actually see condition improvement when switching to a little more protein than "layer". And 22% protein was shown to give the highest hatch rate... which to me says better nutrition in the eggs my family is consuming.
