The judge in the £14 million Hatton Garden raid case has been urged to cast aside sentencing guidelines as it was the "worst" type of burglary and a crime of the "utmost sophistication".
Prosecutors submitted that the statutory maximum of 10 years' imprisonment for conspiracy to burgle should be taken as the starting point when considering how long the thieves should be jailed for.
Ringleaders John "Kenny" Collins, 75, Daniel Jones, 61, Terry Perkins, 67, and the group's oldest member, Brian Reader, 77, pleaded guilty to the offence last September.
Carl Wood, 59, of Elderbeck Close, Cheshunt, Hertfordshire, and William Lincoln, 60, of Winkley Street, Bethnal Green, east London, were convicted of conspiracy to commit burglary and conspiracy to conceal, convert or transfer criminal property, after a trial at Woolwich Crown Court.
Plumber Hugh Doyle, 49, of Riverside Gardens, Enfield, north London, was found guilty of concealing, converting or transferring criminal property between January 1 and May 19 last year.
Prosecutor Philip Evans QC asked Judge Christopher Kinch QC to consider sentences beyond those in the guidelines.
He said: "Regarding count one - conspiracy to burgle - it is clear that this was a plan of the utmost sophistication, that was many years in the planning.
"It was designed to achieve the maximum possible return for the minimum possible risk, and, the prosecution submit, plainly fits within the broad range of the worst type of this offence which comes before the court, particularly bearing in mind the low maximum sentence.
"For those reasons the prosecution submit that it would be a) contrary to the interests of justice to follow the relevant sentencing guideline and b) appropriate to take the maximum sentence as a starting point in relation to each defendant on count one."
However, Reader, who was only present on the first night of the raid, could potentially avoid being jailed after falling ill in prison.
Also known as "the Guv'nor", he suffered a stroke in Belmarsh and "may only have months to live".
His barrister, James Scobie QC, said the pensioner was too ill to even appear via video-link from the high-security prison where he is being held.
He added: "He had what turned out to be a second fall in Belmarsh prison, which resulted in him being left for two days without proper care and then ultimately ending up in a critical care unit at Woolwich hospital, having had a stroke."
The court heard that Reader also has a history of prostate cancer, was treated for septicaemia, and has a potentially cancerous mass on his face.
Asking for his sentencing to be adjourned, Mr Scobie said: "We suspect the prognosis for him, long term, is poor.
"And by that I mean it may well be that some of the concerns that we have been told about by making inquiries are such that it may well be that he does not have many more months to live, then the court should be made aware of that."
Mr Scobie also said Reader's recovery had not been aided by the nine armed officers who guarded him in hospital.
Judge Kinch excused Reader from the hearing and said he would revisit the matter on Wednesday, once more information on Reader's condition had been obtained.
The other six men appeared in court, flanked by 12 dock officers, and sat silently as they listened to updates about their accomplice's health.
The gang carried out the "sophisticated" and meticulously planned break-in over the Easter weekend last year. They ransacked 73 boxes at Hatton Garden Safety Deposit after using a drill to bore a hole into the vault wall.
Another thief, known only as Basil, remains at large. He was instrumental in helping the gang get into the vault in the heart of London's diamond district.
The gang who broke into the vault included participants of some of the most notorious heists of the last century - Reader had been involved in the £26 million gold bullion Brinks Mat robbery, and Perkins was a player in the £6 million Security Express raid.
But despite their experience in acquisitive crime, it took the bungling "Bad Grandpas" two nights - April 2 and April 4 - to breach the vault, and they were caught after covert recording devices captured them boasting of their endeavours.
Collins's decision to drive his own white Mercedes on reconnaissance to Hatton Garden led to a breakthrough in the case, when police saw it on CCTV and were able to trace its movements.
Collins, of Bletsoe Walk, Islington; Jones, of Park Avenue, Enfield; Perkins, of Heene Road, Enfield; and Reader, of Dartford Road, Dartford, have been in custody since their arrests.