I just asked this question on the OE facebook group, what to call OE that are F1 crossed out to another purebred that is not one of the breeds used to produce that particular F1 bird. For example, F1 BCM X CCL bred to an Isbar, etc. I'm calling them F2 because I don't know what is technically correct. I also do BC1 crosses back to the Marans, but about 85% of people don't know what I mean. *sigh*
There's an OE group on Facebook?