I hear you regarding the sister casino issue. That said, this is also a BC.game problem, because their website links directly to BCPoker, so they absolutely need to have some accountability here.
I got the answer for your case, about half an hour ago, where I was busy writing an essay. They found at least eight connected accounts. Seven actually accessed from the same device. I'd like to hear your rebuttal, and based on what the point of your rebuttal is, I'll ask their supporting evidence to disprove the rebuttal.
You're handling this one properly. You should do them all this way without double blind studies or asking for screenshots of emails.