Personal experience they cannot be sexed at hatch.
Can you explain what you mean by this?
I know some people are sold second generation sex links from private breeders (I use the term "breeders" loosely in this context) ie chicks hatched from sex link parents and the colour-sex linkage does not continue into that second generation, so what they expect to be red pullets are not.
What was your experience? Did you breed your own sex links?