Update on apps used before 10/15
Having seen the advice above that if the mailer code loads your app is good to go, I first tried to use a mailer code that DW used on 10/14, and it didn't load. Then occurred to me that while the app was done before 10/15, it wasn't approved for some days later. So then I tried using a code that I previously used successfully on 10/4, and the app loaded. I'm was at 4/6, last Citi app 44 days ago, FICO 790-810 depending on CB, and 6 figure income, plus what they used to call Citi Gold (not sure if the last part makes a difference).
I got an immediate denial, with a letter to explain why in 7-10 days. I called Recon a few minutes later, and didn't tell the CSR I was denied, just said I didn't get an immediate approval, and was there any information I could give them to get it approved more quickly? CSR asked for my app ID, and I just said I didn't get one, so he looked me up by my SS #. After putting me on hold 2 or 3 times, total maybe 12 minutes, with no questions asked, I was approved for $16,500. Whew !
So, yes, mailers used that got approved before 10/15 can be reused, even by the same person, but apparently only if the app was approved before 10/15 as well.