You are mixing together two distinct processes.
If you merge your ThankYou Rewards accounts the expiration dates of the points will not be affected, and all future points will automatically post to the new ThankYou Rewards account. Citi will still track which points were generated by each card, and if you close a card account those points will expire in 60 days.
If you share some points from your Premier account with your Prestige account the shared points will expire in 90 days.
Premier points are worth $0.0125 when redeemed for airfare. Prestige points are worth $0.0133, except...
...Prestige points are worth $0.016 when redeemed for AA airfare.
In other words, Prestige points are always worth more than Premier points for airfare, but they are worth the most when redeemed for an AA ticket (although not all AA fares are available through travel agencies.)
@Mia,
Please explain a bit more as am bit confused.
You said something like if I merge, it won't expire but if I share, it expires?
I don't know I should call it Merge or Share, What i mean is I have points on both of these cards=Prestige & Premier.
Since I am getting more values with Prestige points on flights, I thought about combining my TY premier points and prestige points. By doing that, my premier points become prestige point? Is that a sharing and expires in 90 days? It is better to combine/transfer my premier points to prestige points if they don't expire in 90 days?
Thanks