''the very armor'' - it's no mystery how Horatio knows that armor.  He saw it on display as part of King Hamlet's memorial exhibits, with an attendant there to talk about the exhibits (and help guard them.)

''the very armor'' - it's no mystery how Horatio knows that armor.  He saw it on display as part of King Hamlet's memorial exhibits, with an attendant there to talk about the exhibits (and help guard them.)

Memorial exhibits are explicitly mentioned in the play, when Laertes returns in Scene 16, and it's also explicitly stated that Horatio returned to Denmark, from the University of Wittenberg, for King Hamlet's funeral.  The memorial exhibits for a King, especially one who ruled for many years, could be virtually like a museum.

Memorial exhibits are explicitly mentioned in the play, when Laertes returns in Scene 16, and it's also explicitly stated that Horatio returned to Denmark, from the University of Wittenberg, for King Hamlet's funeral.  The memorial exhibits for a King, especially one who ruled for many years, could be almost like a museum.

Horatio may have seen that exact armor the previous afternoon, or at any time since his return to Denmark.  Armor is steel, and it does not, of course, evaporate and rise like the dew when it's taken off.  It continues to exist, and can outlive the wearer if it's cared for.  Everybody knows that, or should.  Some suits of armor worn by Henry VIII are on exhibit now in the Tower of London.

Horatio may have seen that exact armor the previous afternoon, or at any time since his return to Denmark.