If that is the case, then Bungie should do something about updating the trophy details for Seal the Deal to make that clear, or just update the trophy to pop for any triumph seal, as the details imply. It wouldn't be any more difficult to do than to update the trophy details for the Leviathan Raid trophies which they have already done. Those trophies are now set to completing a Nightfall strike on Master difficulty and Grandmaster Difficulty respectively, for the record.