http://www.strangehistory.net/2014/02/26/the-myth-of-unbloody-zagonora/
It is surprising, how many read The Prince, and then take Machiavelli as an honest reporter.
As the final sentences suggest, it's possible that there were just a few deaths worth noting with the average mercenary's or citizens soldier's death not being worth mentioning.
Nearly impenetrable body armour combined with a mentality that death was not glorious but instead not very cost efficient could reasonably have led to a much greater ratio of rank and file deaths to noblemen/officers than in other late medieval conflicts.