This is the exact situation we’re in with my daughter’s horse. He was registered in Canada but then reregistered (with a different show name) when imported (a couple of owners ago). No evident fraud involved, all details are correct, just one registry (with an all-Canadian show record) under what is now his barn name and another in the US with his current show name.
Was it worth the hassle to correct it with USEF? I’ve thought about trying to get the records merged but am not sure what the benefit would be at this point - he’s now got a long US track record under the current name and number, as my daughter is a step-down job for him.