With that temporary flag mention before, you maybe meant this post?
Everybody should be able to read the flag and know that the data can be deleted. But they would be able to make that data immutable by storing the data themselves. Only changing the flag of such a (then deduplicated) data chunk would be enough.
Edit: ‘the Everybody should’ is of course assuming the solution of the referenced post. And for me this also has lower priority: first have a good working system with immutable data only.