I just used one of my ancient future cruise deposits. My Celebrity TA had to resubmit the old FCD back to the ship that issued it as the new computer program can’t handle the old certificate. Same thing happened last couple times I used an old certificate so knew what to expect.
My booking, an exciting deal rate, was on hold - and even dropped a bit in price - while waiting close to 36 hours for the new certificate to be issued. Watched cabins drop off the website so was happy there was a cabin hold.
Once the new certificate was issued with a new number, the deposit and OBC from the old onboard booking were applied to my cruise booking.
i believe it is great that one can now see that certificate information. I had more certificates than I realized.