Hi
John! I'll be glad to answer this question for you. Some guests have reported being able to get just one PhotoPass CD in such situations, so technically you could buy the pre-purchase offer for both.
However, since your photos expire thirty days from the time they are entered into the system, you would need to purchase PhotoPass photo extensions for the May visit pictures. As of today, the cost of PhotoPass photo extensions is as follows: $4.95 for a Four-Day extension, and $9.95 for a Fifteen-Day extension. You will need to do the math in order to determine which would be most cost effective. It will probably make more sense if you bought two separate pre-purchase
Disney's PhotoPass Pre-Arrival Savings Offers instead of buying extensions. If you opt for the latter, keep in mind you will run the risk of forgetting to do this and allowing the May pictures to expire before you have a chance to upload and finish making edits to the November trip pictures. On a separate note, since you are purchasing the PhotoPass CD, be sure to ask PhotoPass photographers throughout the parks for Magic Shots. You never know what famous Disney Character will be magically superimposed on your PhotoPass photos! Again, let me know if I can be of further assistance. Have a memorable visit to the Walt Disney World Resort!