I´ve read in Deadpool 02 Wade´s Wilson War where Deadpool states that his body was scarred because after having the serum injected the laboratory a fire arises in the laboratory so he gets burned, after this his serum is "accepted" by his body so he regenerates but regerating factor assumes that his default condition is being burned, so when he heals he has a burned body.
But there´s another version which says:
"Ajax subsequently tore out Wilson’s heart and left him for dead, but Wilson’s thirst for vengeance was so strong that it jump started his healing factor, regenerating his heart, although not curing his scarred body"
Which is the real one? and why there´s more than one version? and which is the good one?