Lost of relationships between two different projects?

Hi, first sorry for my English.

We have a dude in our Scheduling team, we’ve two programs (one engineering and other construction), we realize back ups every days but of each one not the sum of them. The problem is that when we have wanted to restore one part we have lost all the relationships between them, because we only have the back ups of engineering or construction. I think than if we do a back up in sum there not will be any problem, but someone knows how to recovery the lost information we had?

Thanks for your time, i´ll very pleased with your help.

Best regards!!