A pure Black Copper Marans chick would carry two copies of the Birchen Color pattern and would written as [eR/eR]. They should NOT have any red color in the wings.
An incomplete Black Copper Marans would only carry one gene for the Black Copper coloring and therefore is not pure bred for the black copper colors (but is still a Marans). It should show red in the wing tips at about 2-4 days old if it has the Birchen Color pattern. It is written as [eR/eb], [eR/eWh], or [eR, e+] depending on what recessive color is it carrying.
An incomplete should show red in the wing tips at about 7-10 days old if it has the Extended Black Color pattern. It is written as [E/eb], [E/eWh], or [E/e+] depending on what recessive color is it carrying.
Note if you breed a cockerel that is [eR/eR] to a hen that is [eR/eb] and a hen that is [E/eWH] then the out come of offspring could be [eR/eR], [eR/eb], [eR/eWh], [E,eR].
Those that are [eR/eR] would likely produce hens with faint copper on the hackles. Those that are [eR/eb] and [eR/eWh] would likly produce hens with good copper on the hackles, and those that were [E/eR] would likely produce hens that are black with no copper on their hackles at all. Until you get the recessive color out of the breeding if is very difficult to improve the copper color on the hens because you don't know which ones are produce the best copper color with a correct primary color pattern. To make it more complicated an [E, eWh] would look like an [eR/eR]. So...leaning to sort what you have goes a long way. Once you have eliminated the incorrect color patterns from the flock you can achieve a high degree of consistency in you flock. Before that you are likely to see a lot of variation in the offspring. Again if you aren't breeding them it doesn't really matter. If you are breeding them you spend a lot of time studying them and taking notes and with every cross you hoe that you see better consistency that you did with the previous breeding group. Most people feel that all the details and work are a royal pain. Chicken breeders that do this for hobby actually enjoy the challenge of figuring things out to be able to produce uniform flocks through their selective mating.
Most of what I have learned are things that my mentor who has been breeding BCM for over 12 years figured out first and then I just verified in my flock to see if we both got the same results. 
