Judge Mark Brown, sitting at Liverpool Crown Court, said the recent changes to the law that increased the maximum sentence for people who allowed a dog to carry out a fatal attack on a person do not apply to this case.
The tougher penalties, which mean dog owners can face 14 years in prison, were brought into force last month but Sulley and Woods' offences predate that ruling.
The judge can only sentence in this case according to the old guidelines and not retrospectively.
More top news
Breezy and wet tonight as rain sweeps in from the west meaning a miserable start to Sunday morning.
BBC Political Editor Nick Robinson has revealed Labour tried to recruit him to be Ed Miliband's spin doctor in the run-up to the election.
Nasa has begun its countdown for a mission to discover whether life might exist on Jupiter's moon Europa.