Well if that isn't the truth! But generally speaking ecosystems tend to exist long enough for certain phenotypes to stay the same for while. Or millions of years, looking at you coelacanth and horseshoe crab

. I do think I have read you writing you do add new breeds every once in a while, so guess it's always changing how exciting!
That's how I understood it too. In your specific flock I would think most should be heterozygous and the specific rooster just didn't inherit that gene.
But you do raise an interesting question. I only know the theoretical stuff which suggest that Polish are homozygous well all the other smaller crests are heterozygous. I have seen some small variation in crest size, as the farther my flock went from their Polish ancestor the smaller the crests became. But this homozygous and heterozygous view seems to suggest cream legbars, brabanters and spitzhauben are heterozygous. So maybe there are indeed multiple genes going on behind the scenes, or the smaller crests of these breeds could be an ancestor version of the Polish one and are therefore still homozygous?
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Showing this image from a
paper that created a taxonomy of old Dutch breeds. Sadly it doesn't show other European breeds. there are 2 Polish breeds listed as Polish bearded tends to refer to Padovana, which is a seperate breed.
Don't know much about double spurs yet. But I do know they are very hard to psot on females. So somewhere you did get a double spurred chicken and if that was a long time ago then its only been inherited by the hens so far, until now that is. If you are able maybe check your hens and see if you can spot an indication of double spurs?