It matches the known proof die for 1875, but that's meaningless, since the business strikes used the same die. The denticles have the same appearance. It may, in fact, be a Proof, but if so, it's been mechanically cleaned or other wise altered and would be an "impaired proof." Certification is a must as even an impaired proof is worth a few hundred bucks.
The presence of wear, by the way, does not automatically mean that a coin is not a proof.
I would not call it a Proof unless it had been certified; I think that as stated it's almost certainly a business strike; 36K minted @ Philly in '75 but only 2.4k proofs.
How did you come into possession of the coin? Most 20 cent proofs have some degree of cabinet provenance.
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