I posted a response before I had carefully re-read your entire post. I think the key to this is the part where you say you "removed the VM's from Active Directory and from vCenter Server using the vSphere Client and by browsing the datastores when needed." While the ADAM and Composer databases had no remnants of the VMs left in them, it is possible that there is still some piece of VM7 left in the vCenter database that's causing Composer to see it as already there. I'm no SQL DBA, so I'm not going to presume to give any instructions on how to fix that, but if you have anybody there with the right knowledge and skills (or if you're such a person) you may be able to ferret out the offending record and get VM7 back again. It's someplace to start anyway. I hope that helps.

Dave