I could have this all wrong - but in a way, From what I understand the ones that truly will be Silverudd's Blue will be traceable back their ancestors in Sweden - which probably means that they would be in the 'Studbook' (certainly over there -- and one would need to be developed for here)---
To my knowledge, There aren't rumpless Isbars. So to become rumpless, someone must have either mixed up eggs and gotten an Araucana and thought it was an Isbar or there was some crossbreeding happening.
Here is a thread that talks about that -- I just read a bit of it:
We are calling our own USA Blue Isbars Silverudd's Blue partly in homage to the name change that KYTinpusher told us about which occurred in Sweden the weekend before Easter.
-- When people have barnyard oooops events and a roo jumped a fence, it could be that the resulting chick is only 1/2 the breed under consideration. They may or may not know about it -- but sometimes some of the Isbars that have been presented don't seem like they are actually Isbars IMHO.
What makes a true Isbar?
what we have is:
1. green egg laying,
2. single comb
and that certain graceful and streamlined look of the Isbar -- most of us appreciate the super-dark almost black-looking eyes.
When a breed becomes very popular, rare, in short supply and high-demand -- there are a lot of people who hop on a bandwagon to produce a lot of that new breed to collect revenue. Some of this happened when the Cream Legbar first became popular in the USA and many people got "Cream Legbars" that perhaps weren't. Some sellers changed the breed name to Creme Legbar or Crested Cream Legbar -- so maybe they weren't REALLY passing off a bird that wasn't because the name didn't match.
Chickens are so complex and the genetics are complex, so there isn't a real way of knowing all that goes on -- and I don't want to disparage anyone's chickens that has listed variances here -- that isn't my point....
How does a group of people who has interest in a breed like this one, that is beautiful, rare and maybe even a bit in danger -- keep the true birds going into the future?