I just skimmed through 25 pages of Circo infant and toddler clothing at target. all the little shirts and shorts I looked at were 100% cotton, as I thought they would be. The shirt and shorts would be similar weight and disintegrate at a similar rate, being exposed to the same environment. The lettering could be a different material, though.
If Casey had killed her and put her clothes in a different place than her body then her statement about not finding the clothes might be incriminating but her clothes were with her other than the body of the shirt and her shoes. This statement, to me, sounds like a mother imagining the worst that could happen to her daughter, thinking the killer might have raped her, carelessly leaving her clothes somewhere when he ran off. If she had left the usual couple of changes of clothes with her when she last saw her, those clothes are still missing. No, I'm sure Cindy doesn't recall every piece of clothing exactly. I've had things disappear and didn't even know it till they showed up in some strange place. The phrase on the shirt doesn't concern me either, only that it is there and not the body of the shirt.
Eddeva, are you saying if Haleigh would have been found in that dumpster that no important evidence could be found with her? They would simply have to sort out all the DNA and clear each person. There could also be other items of interest connected to that spot in the dumpster or landfill. LE in the Sandra Cantu case were sifting the landfill.