On Wednesday Judge Gemma Loughran, who told the 64-year-old, "if you are not the worst serial sex offender in this jurisdiction, you are certainly one of the worst", ruled that given the 'principal of totality' she would not add to his sentence.
The Dungannon Crown Court judge, said while McDermott would receive consecutive sentences of three months on each of the four charges committed against his ninth victim, that total sentence of 12 months would be concurrent to the jail term he is presently serving.
Judge Loughran, quoting from an earlier court hearing, described the sexual abuse of youngsters he and his brothers meted out to their victims, as "pernicious", adding that they had "wreaked havoc" on the lives of children, some of whom blamed themselves for what happened, while in fact that blame fell squarely at the door of the abuser.
This is the fifth time in four years that McDermott, who along with his three brothers unleashed a 35-year "tidal wave of abuse" on their quiet village of Donagh near Lisnaskea, has been before the Crown Court for either indecent assault or gross indecency.
Last December McDermott, from Moorlough Road in the village, pleaded guilty to four charges of indecently assaulting a teenage boy, between April 1997 and 2001, when aged 13 to 17.
Judge Loughran said the victim, came forward last April with his complaints after seeing a BBC programme on the brothers, in which it was said there might be more victims, and he thought "he might be one of those others".
McDermott was originally jailed for nine years, in June 2010, before being given an additional six months in October 2011, followed by a further six weeks term in September last year, before being finally given another consecutive sentence of three months in April last year.
On completion of the sentence, he will serve a further three years on probation.
He was the only one of four brothers to have stood trial for the sex abuse they had all meted out to a number of Co Fermanagh youngsters.
Originally two other brothers, 62-year-old James McDermott and 54-year-old Owen McDermott, were to have stood trial with him charged with sex offences committed during the 1970s and 80s.
However, they were deemed unfit to stand trial because of their mental disability.
A fourth brother, 62-year-old Peter Paul McDermott, took his life the day after he went on trial for his role in the abuse, abuse which the original trial judge, Judge David McFarland said, had turned what was "a quiet picturesque village in Co Fermanagh into a village that had an appalling secret, and it was the children who bore the brunt of the tidal wave of abuse".
Judge McFarland said the "deviant" McDermott brothers had between them "stolen" the childhood of their victims, subjecting them to "horrific" abuse, although "some, of course suffered more than others, some for longer period, and some were abused by one or more brothers".
McDermott's original sentence of nine years in jail, plus three years probation, followed his guilty pleas to a total of 35 offences, involving the abuse of, four boys and a girl, including the rape of a schoolboy, committed between 1969 and 2001. His remaining victims were all boys.
He is due for release from prison in August.