The pardons would not be in the record. They would almost certainly be classified and sealed.
In theory, it could remain sealed forever if they never had to use it.
DOJ does not have to approve a pardon. The president can pardon a person for any federal crime, without approval from anyone.
"But could President Trump really pardon someone in secret? The short answer: In theory, yes.
In general, pardons are vetted by the Office of the Pardon Attorney in the Justice Department. But the regulations governing that process don’t interfere with or supersede the president’s constitutional authority on this issue, which mentions nothing about needing to notify the public of a pardon."
time.com/4933386/donald-trump-secret-pardon-law/
Some were advocating to 'abolish all prisons' earlier.
If you cannot show a specific law, code, or regulation that prohibits making a pardon classified, than there is nothing that would prevent it. The entire record of it could be classified.