Here is the story so far:

1. A client hired us to do an iPhone app for them. This client had never done an iPhone app before and as part of the arrangement we handled all aspects for them, including app store submission, and we handle some level of future development (new features, bug/security fixes, etc.)
2. We created a Distribution certificate and key pair on the client's behalf
3. We developed the app, published it to the App Store without incident
4. Some time later the client hired a second developer to do a different app for them
5. This second developer, it appears, has revoked the existing Distribution certificate and created a new one with a new key pair on their system
6. This second developer shared the new Distribution certificate and key pair with us for future reference.
7. Due to user error, this new certificate and key pair has now been imported onto the Macintosh where the original certificate and key pair for the original app we developed were created and the originals were not backed up.

So we have

• App #1 on the App Store with Distribution certificate/key pair #1
• App #2 either on the App Store or soon to be using Distribution certificate/key pair #2
• Distribution certificate/key pair #1 appears to be lost now

So my question is: if we ever need to update App #1, will we be able to, using Distribution certificate/key pair #2? Or will we have to upload it as a new app?