I have a stack of mailers from the past 10 months.
The mailer that I have that HAS the 24 month language is a 9 digit 50k offer with the Citi.com/applytodayAAplatinumselectcard.
The 12 digit mailer with no 24 mo lingo is Citi.com/applyAAplatinumselectcard.
The 9 digit mailer with no 24 mo is Citi.com/applynowAAplatinumselectcard.
I did have some 9 digit no 24 mo mailers die on me prematurely last fall. I tried to use them at the 40 day mark and the two I had, that had never been used were dead. Hope this helps.