I had a case when travelling with someone on a separate booking. I was Diamond, he was Gold. We checked in at BKK together and the agent said that they would upgrade me but they weren't upgrading Golds yet. He said I could take the upgrade and take the chance that my friend would also get upgraded or not. So I took it, and in the end in the lounge we were told my friend got upgraded also, but we weren't sitting together.