The tragedy, in May 1992, led to the council revising its fire safety training for all social services officers.
But the local government ombudsman report into the fatal blaze, published this week, says the council should have taken action sooner and was almost certainly directly responsible for the deaths.
Three care officers took seven young people with varying degrees of learning difficulties, some severe, to the cottage on the slopes of Snowdonia for a short break in May 1992.
All the care workers had been drinking together that night. The events leading up to the fire are unclear, but one of the officers told the ombudsman he was woken by his colleague dashing into the bedroom screaming that the place was on fire some time in the early hours.
He said they tried to open a window which was meant to be the fire escape but the chain inside the glass tube which released it was missing.
Finally they escaped and led the others to safety. But one woman, aged 20 but with the mental ability of a two-year-old, and a man, aged 22, were trapped inside.
Emergency crews arrived too late to save them and they died in the fire.
Two of the officers were hospitalised with their injuries for several weeks and the third received counselling for psychiatric problems caused by the tragedy.
Two months after the disaster, Wirral MBC produced a leaflet for staff called Safety guidelines for overnight accommodation.
Finding maladministration with injustice by the council, the ombudsman, Patricia Thomas, described the fire as 'an appalling tragedy'.
She said: 'The council had no procedures to check the safety of the accommodation. 'If it had checked, it is unlikely the party would have stayed at the cottage, and the tragedy would not have occurred.'
The council was told to make a payment to a charity chosen by the victims' parents.