Dinosaur,
After reviewing the video you shared, I have to share a couple of notes.
First, it's a well-known phenomenon, though not common, that a hen can visibly change sex to become a rooster--sort of. Some good pictorial examples on Feathersite.com:
http://www.feathersite.com/Poultry/BRKChange.html
and a good explanation on the land grant universities site:
https://articles.extension.org/page...in-chickens-kept-in-small-and-backyard-flocks
I have raised Crevecoeurs since 1997, and have never seen this sex-reversal in a Crevecoeur, so you might be the first to document it!
Second, I think I understand better why you are saying you see smaller crests on your Crevecoeurs than on your Polish. There is a naturally-occurring sport for the Black Crevecoeurs that produces a nearly-white Crevecoeur. I have one of these white Crevecoeurs from Jeannette Beranger at the Livestock Conservancy. It seems likely to me that the white and other related blue and splash Crevecoeurs could have been bred out of natural sports. These sports would be Crevecoeurs in every way, except that they would be a different color than the usual black.
However, if you cross out your Crevecoeur with a chicken of a different breed to pick up that breed's color, then the birds you get as a result of that cross would have smaller crests, especially if the birds you crossed to, as in the lavender Ameraucana in your photo, have no crest. (In other words, crested bird crossed with non-crested bird results in smaller-crested bird.) And those birds would be Crevecoeur mixes, not Crevecoeurs.
The Crevecoeurs are rare. Most people breeding exhibition birds are not really interested in maintaining the breed standard; their goal is to create a bird they can show and win with. People who are maintaining the breed for its heritage values may also show, to get confirmation that their birds are true to the standard. However, they are not outcrossing their flock to another breed in order to achieve a rare color, or even to maintain a characteristic of the breed using a different breed.
To give an example, runner ducks were originally white. Now the colors include gray, fawn and white, black, trout, etc. These colors were achieved by crossing a white runner duck with a duck of another breed who had the desired color. Years down the road, my gray runners look a lot like the original white runners, but they are smaller, and have some characteristics (not the erect runner stance) of the other parent breed that lent them their color. When you see runner ducks compete at a show, the champion is usually a white. Why? Because the colored runners do not have all of the runner characteristics of a white runner duck, especially the stance, face shape, and size.
So, you could, for example, decide to breed for a Crevecoeur mille fleur. You would want to select the chicken breed that is closest to the Crevecoeur but already has mille fleur colored individuals to use for breeding. Once you are successful in crossbreeding to produce individuals that look like Crevecoeurs and also have mille fleur coloring, you will want to breed back to Crevecoeurs, to get as close as possible to a Crevecoeur while retaining a mille fleur coloring. Then you will have a Crevecoeur mille fleur.
But wait, will you really have a Crevecoeur mille fleur? You may have all the characteristics that make the bird look enough like a Crevecoeur mille fleur for this generation, but there will be hidden characteristics that may pop out in future generations.
Every good breeder, and especially the good breeders of heritage birds, worry about the long-term intrusion of non-breed characteristics due to mixes from amateur breeders who don't take their responsibilities seriously.
Hello! I m a breeder of the Crèvecoeur from Europe, Germany. I just come up with my YouTube Channel where I presend topics for breeding and keeping chicken. Today I released my first english Video. You can see every color breed of mine in pictures and videos. If you like me to make more of it in english, please let me know.
You can search for it with: Crowing hen Dinosauer
https://youtu.be/moEeb-jPMzI