I don't know that we really need to apply Sherlock Holmes' Law in this situation. (After eliminating the impossible, whatever remains, no matter how improbable, is the truth).

Perhaps he drinks the cognac in tribute earlier in the day and then steals in to leave it for Mr. Poe after he is sober.
Or maybe he leaves a full bottle and the curator, Jeff Jerome can't say no to a good bottle of cognac.