Is it possible to let git-annex check and update the "number of copies" or "whereis" information without recalculating the checksome?

The use case is this:

I have a very large "repo1": 300.000 files 1.5 TB.

I copy it using low level tools for performance (clone the partition, netcat over network, or whatever...)

Then i do "git annex init 'repo2'". All files exist in both repos and the simlinks are valid, but git-annex does not know about it. The "git-annex wehereis" only shows "repo1". How can I tell him without rehashing 1.6TB?