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
A global unemployment rate of 50% is possible as job vacancies are filled by machines, according to scientist Moshe Vardi.
A British teenager arrested in connection with cyber-crime offences is suspected of hacking an email account used by the head of the CIA.
A man who hit a 13-year-old boy leaving him bedbound for life has been jailed for three years.