sword of gryffindor

[leb2323]

No: HPFGUIDX 81388

I was just rereading the series through again (for the umpteenth
time) when I developed a nagging question that I cannot seem to
answer for myself.  In GoF after Harry has the dream in divination
and heads off to DD's office he is left in there alone while DD, 
Fudge, and Moody leave to examine the grounds (ch 30 -- the
pensieve). There is something of an inventory in the narrative
listing all of the items that either have been or will be important
in the story -- Fawkes, the headmasters' portraits, the sorting hat, 
the sword of gryffindor, and the pensieve.  

The sword is displayed in a glass case.  My question is, was the
sword always on display in DD's office or did Harry summon it out of 
thin air when he literally pulled it out of the hat in CoS and now DD 
has it encased as an heirloom keepsake.  Since the hat and the sword 
both belonged to Godric then it could be plausible that it 
materialized from nowhere instead of being summoned from DD's office. 
 
Any theories on this one or at least a nudge to the blatantly obvious 
passage answering the question that is probably in the books
somewhere that I just overlooked?

leb