Hello Jose, As far as I can tell without completely disassembling the hilt is that the guard is more than likely original to the bolo, and if not it has been on it for quite a while. While the patina on the guard, grip collars and butt plate match perfectly to each other it is always possible that the guard could be a later addition. The main reason that I believe the guard could be original is that I see no evidence of the hilt ever being shortened to allow for the space needed for the guard. My best guess would be that looking at the poor peening of the tang that it might suggest that the hilt could have come loose at some point and been reattached in a hasty manner with the guard accidentally being installed in an incorrect position but this is only speculation on my part.
Robert