Datapoint. I applied for new Premier card through the Reddit 50k/4k link on 10/25/2017.
Prior to applying, I sent message via secure message to Citi CS confirming my eligibility for getting new Premier signup since my last Preferred/Premier/Prestige opening/closing was March 2015. I got confirmation I should be eligible.
I was approved for Premier card 2 weeks ago and the page my new Premier card came in mail in had verbiage "Our records show that you are not eligible for the bonus offer based on a recent opening or closure of your Citi card(s)."
I called Premier card CS, agent said he'll forward my sign up bonus eligibility to Citi research department and they'll look into it and send me a letter in 2 weeks with their findings.
Today over Citi secure message, I then got message saying reason for my being ineligible for the Premier 50k sign up bonus was because the Citi Thankyou Forward Card also counted for the 24 month rule in addition to the ThankYou Preferred, Premier or Citi Prestige card listed in the app 50k sign up bonus T&C.
My 8 year old Citi Thankyou Forward card was closed for inactivity in Oct 4, 2015.
The funny thing is, I applied for my Premier card on Oct 25, 2017 which would have been over 24 months from the Forward card closure date. I responded to that effect via secure message. Now to see if Citi CS can see reason.
In meantime, beware the new development Citi seems to be looking at Forward card dates as part of the Premier sign up bonus eligibility.
My fear is the Citi ATT Access more card (which earned TY points in addition to the $600 phone sign up bonus) would also count for Premier's 24 month rule because I closed the ATT card 1 year ago.