I have two Blue Cuckoo Marans from Meyers and a Blue Andalusian. The two Cuckoos are different in color, size and comb. One looks almost identical to the Blue Andalusian except for the Andalusians large comb. I can post photos if you are interested.
I love answering questions. My dark blue lady has many feathers on her feet. The lighter one has 1 on each foot. They never had a Cuckoo pattern but if they are out in the sun, and it shines just right, you can see it like a shadow in their feathers.
"Cuckoo" is supposed to have white barring across the feathers.
I see that Meyers sells three kinds of Marans with blue: Blue Copper, Blue Cuckoo, and Blue Birchen.
https://meyerhatchery.com/products/Blue-Copper-Marans-Day-Old-Chicks-p213412049
https://meyerhatchery.com/products/Blue-Cuckoo-Marans-Day-Old-Chicks-p212598964
https://meyerhatchery.com/products/Blue-BBS-Birchen-Marans-Day-Old-Chicks-p213412046
Are you sure you have the cuckoo version, rather than one of the others? Cuckoo chicks "should" have a pale spot on top of their head (which I do not see in your photos), and the adults "should" have white barring in their feathers. I say "should" because sometimes it is much more visible than other times. If you ordered them as Blue Cuckoo they probably are, but if you ordered an assortment and then tried to identify what they sent, you might actually have one of the others.