They do not start out single comb. You should be able to see a difference as soon as it starts showing. If it has a closed comb that is very poorly shaped I guess it might look somewhat like a single comb, but that is a DQ and should definitely not be used for breeding. If it is the SBB you should be able to tell sex between 4 & 6 weeks because the cockerel will start growing in red on the shoulders & wings. The pullet will stay evenly spotted with brown.I thought mine was sicilian buttercup but mine has a single comb and since Ideal has the largest color vatiety of OEGB I am sure mine at least is silver campine OE. Unless the buttercups start out with a single comb?? I have never had them before, can you enlighten me/us..?