In the past, on more than one occasion, when the VA sent a CSA marker with an incorrect inscription (their mistake), we asked them what to do with the old marker when we got the replacement, and they said to destroy it. So we did, and buried the remaining chunks of marble. Not easy, but they didn't want it back and wouldn't pay to ship it back.

I have also seen what looked like an old VA marker, broken and on the banks of a lake, when that soldier's marker put in by the SCV on his unmarked grave was still there and in good shape. How that broken marker got there, we don't have a clue (and no clue that another marker even existed).