The warrant applications may be sealed.... but surely Cohen demanded a copy of the Warrant issued for his “seizures”. They could not refuse him a copy of the Warrant.
Anything else and this is the Geheim Staats Polizei-== GESTAPO tactics.
Yes, he received his copy of the warrant. Which is useless in defending yourself from it. You need the affidavits of probable cause the warrants were based on and keeping them sealed prevents or delays quashing the search warrant and buys them time for the copying of the seized files.
There is absolutely no good reason to seal the affidavits except to create delay and to keep the public in the dark.