Just some advice for the newly engaged.
I got engaged last New Year's Eve. When FI bought the ring from Zales, they didn't have the certificate for the ring in the store and told us to pick it up later. We took the ring to get sized the day after he proposed and it slipped our mind to ask about the ring certificate. When we took it last week for the Dec. cleaning, we remembered to ask for the certificate. Since the ring had been sized, the lady at Zales couldn't make out the full serial number and the serial number wasn't on the receipt like we thought. When we take it in for the June cleaning they are going to send it back to the factory where they will either check what is inscribed in the diamond or re-do the appraisal which will take about a month.
Try to have them right down the serial number before you get it sized if they don't have the certificate at the store when your FI purchases the ring.