I understand what you are going through with the Marans. I bought several dozen eggs two year ago just for a test on Marans eggs from different people claiming to have good BC Marans. We kept no male and only seven females from all that we hatched. When buying sight unseen there is no way we can see what we might be able to get.
Be very careful with the lower body brown feathering.
Don, I'm fairly certain that as you said, my BCM are from a black/blue program. I've seen where you say it's fine to breed these together, but don't breed them to the pure BCM. When I start breeding and selling chicks, how do you ethically advertise them? As black/blue/splash varieties?