I think I read somewhere that they'll be scoring accounts with very small limits lower than others. Perhaps that's what they mean by subprime in this case?
Happened to me too, earlier this year. I called and canceled Gold. They closed it and credited the remaining AF. When the Platinum reported, it showed the original opening date from the Gold.
Missed those threads. But I probably didn't lose any history because the gold should report "Closed by consumer" for ten more years. And the opening date of the platinum does show the original gold date (which was several years ago).
I applied for Platinum about a month ago. The message said to allow 14 days for processing and delivery, but the card arrived in less than a week. It didn't show up on the status page until the following day, though.