Pressed on whether the death toll could climb to triple figures, McCormack said: "I've said I believe it could increase, I don't think it's going to be triple, no."
A 6-month-old baby was among the latest victims to be identified, found dead in her mother's arms in the smoke-filled stairwell.
Westminster Coroner's Court opened and adjourned inquests into seven Grenfell Tower victims, including baby Leena Belkadi and her 8-year-old sister Malak.
As the vast criminal investigation into the fire continues, 60 organisations have been identified as having a hand in the tower's refurbishment, which is suspected to have aided the spread of the blaze.
Prime Minister Theresa May confirmed today that 120 tower blocks across 37 local authority areas have flammable cladding on their exterior.
Efforts to establish who was missing in the wake of the fire were focused on talking to friends, families and neighbours of those in Grenfell Tower, McCormack said.
A list of tenants provided to police by the Kensington and Chelsea Tenants Management Organisation, which managed the building, was "not accurate", she claimed.
"We are many months from being able to provide a number which we believe accurately represents the total loss of life inside Grenfell Tower.
"Only after we have completed a search and recovery operation, which will take until the end of the year.
"What I can say is that we believe that around 80 people are either dead or sadly missing and I must presume that they are dead."
The 23 flats which were said to have no survivors were spread between the 11th floor and the 23rd.
Around 10 flats remain too perilous for police to venture into for thorough examination.
Amid mounting distrust of the official death toll, McCormack stressed "every imaginable source" of information about who was in the building had been examined, "from government agencies to fast food companies".
She said: "What we know is that it would be impossible for anyone to produce a list to show exactly who was at Grenfell Tower that night, that includes the people who were living there or who were visiting."
A couple who were missing and assumed dead had actually been on holiday at the time of the blaze, according to the detective.
Referring to the criminal probe, which has set out to establish if charges including manslaughter will be brought, McCormack said: "We are continuing to seize material on a daily basis and the number of companies and organisations that we know so far had played a role in the refurbishment is over 60."