Then you can run things like:

  guix gc -R $(guix build git | head -1) | grep openssl

and compare with:

  guix gc -R $(guix build git --no-grafts | head -1) | grep openssl

There should be exactly one ‘openssl’ reference in both cases; in the
first case it should be the replacement, and in the second case the
original.

Feedback very much welcome!

Ludo’.