I SM'ed inquiring about my 50K and got this very interesting response:
You are eligible to receive 50,000 bonus points for only one Platinum Card account.
This is because bonus point is issued only once during Cardmembership, irrespective of the number of Platinum Card accounts established/opened in last 12 months.
I see that you had a Platinum Card (ending in xxxxx), which was cancelled as per your instructions on 08/12/2012. 50,000 bonus points were issued on 8/12/2012 on this Card account. I suspect that if you receive 50,000 bonus points you will cancel the card soon. Therefore you are not eligible for the bonus.