Changelog when migrating VCS server

I have been looking into migrating the company Plastic SCM server from an old machine to a new one.
During test migrations I noticed that I could get all the change sets from plastic into the Change Log, but only the first time for any given repository name.

All subsequent migrations to a repository with a name that was already attempted would result in an empty Change Log, even though the repositories were deleted between migrations and new configurations and VCS roots were create. 

This makes me hesitant to just perform the migration, as any mistake will mean that we lose the ability to build older change sets without messing with the content of the repositories.

Is there some way to make TeamCity forget a repository name that it has been connected to such that it would register the change sets when migration the Plastic repositories? 

P.S. 

The steps used were more specifically:

1. Download the repository from the plastic server with:
   cm clone <repository name>@<old plastic server> --package=<local path>
2. Create new VCS root pointing at the new repository
3. Attach the new VCS root to a configuration
4. Create the new repository with:
   cm repository create <repository name>@<new plastic server>
5. Populate the new repository with:
   cm pull --package=<local path to repository file> <repository name>@<new plastic server>