Just got off the phone with a wonderful CSR. Mentioned 5748 and she told me I did not need to call, it was automatic for me. Upgraded from gold-->plat on 7/29/11. (Never heard of this offer being automatic). She said she would note my account, and if for some reason the points didn't show in 8 weeks, to call back and they would just credit the account.
Seems easy enough. Guess I'll have to wait 8 weeks to find out.