> Hashing the data that's added to the archive and then putting the hash in the blockchain would reasonably prove the data in the archive hasn't been modified at a later date.
Here have yourself a timestamp https://petertodd.org/2016/opentimestamps-announcement
https://github.com/opentimestamps/opentimestamps-client
pip3 install opentimestamps-client
ots stamp myfile.txt