Absence of evidence is evidence of absence?
In the case of an armistice, perhaps so. You don't think that the armistice that ended WW1 was misplaced or not entered into the record, do you? An armistice is a big deal and would've been entered into the record if it was official and signed. The fact that it wasn't leads me to believe it wasn't official, but just some kind of non-formal verbal arrangement the Bushanan Administration made to stall for time until Lincoln took over.