Hi, wanted to add a little background info here if it helps. I’m the director of the Veterinary Terminology Services Lab that is tasked with maintaining the veterinary extension. In 2014 IHTSDO decided to move all veterinary only content out of the International release and into our veterinary extension (VetSCT). A large mass of content was moved in 2014, but they continue to find veterinary content on a regular basis and transfer them to our extension. The breed concepts are one example of this. These transfers do in fact nearly always have references to replacement concepts depending on when the transfer was made. There are a few instances where the content was truly inappropriate and no replacement was created.
Up until a couple of years ago (I apologize, I didn’t note the exact date when this change occured), when concepts were transferred from the International Release (core) to the extension, the core concept was retired and a new extension concept was created to replace it (with an extension identifier). We would then create a historical relationship that related the retired concept to the new extension one (this would be in the historical relationships refsets in the extension data).
A couple of years ago, IHTSDO decided that there was no need to create a new extension identifier, that we could retain the same identifier and just have it move from core to extension. In those cases, there is no need for a historical relationship, as the concept identifier is just moved into our tables with relationships, descriptions etc, in the extension. There are still occasionally incidents where there will be historical relationships however, because occasionally there is already an extension concept that has been created and we allow the core concept to remain retired and create a historical relationship from the retired concept to the extension one.
I hope that information is helpful. And if there’s anything I can do to aid in getting the VetSCT content updated in Pallas/Athena, please let me know. We release updates every April 1 and October 1.
~julie