Last month the BBC revealed there had been 14 claims of bullying at the State Hospital at Carstairs since 2010.
The hospital has now said that not all data had been uploaded to its register and the true figure was 29.
Carstairs employs 700 staff to care for about 125 patients whose mental health issues make them dangerous or violent.
The revised figure means that Scotland's minister for mental health, Jamie Hepburn, was not aware of the true extent of bullying problems at the hospital ahead of its annual review in September, at which the facility's performance was discussed.
State Hospital chief executive, Jim Crichton, said: "The information provided for the annual review was based on summary data which was held at that time."
Andy Hogg, assistant general secretary of the union POA Scotland, which represents many staff at the State Hospital, said: "This news does not surprise me.
"The figures are unacceptable and provide sufficient evidence for the State Hospital board to explore this in further detail."
A  spokeswoman for the Scottish government said it had been assured that the State Hospital "is taking the issue of bullying seriously".
The hospital has been under new management since the departure of the previous chief executive in 2013, following a row over thousands of pounds worth of "danger money" which was awarded to board members even though they did not come into contact with patients.
Several members of staff recently contacted BBC Scotland to say that those accused of bullying were still in post.
The State Hospital said that the 29 complaints related to 24 individuals.
Eight members of staff received an official warning over their behaviour.
The hospital refused to say whether any staff had been promoted, despite being the subject of complaints.
BBC Scotland has also seen the results of the staff survey for 2013, which was completed by 60% of the workforce at the State Hospital.
Some 25% of respondents said they had been bullied or harassed by a manager.
A similar figure also said they had been bullied or harassed by a colleague.
The survey suggested that staff at Carstairs were significantly more likely to report bullying and harassment compared to the rest of the NHS.
A report commissioned last year by the chair of the hospital board said bullying was a "running theme".
Sickness absence rates in some parts of the workforce are also twice as high as the Scottish government target of 5%, a situation which management at Carstairs have acknowledged is unsustainable.
A Scottish government spokeswoman said: "NHS boards, including the State Hospital, must have robust local bullying and harassment policies in place, based on national standards.
"The Scottish government uses a wide range of measures to understand the workplace culture within a health board, including the NHS Scotland staff survey. At its Annual Review last month, the Minister, Jamie Hepburn, was assured that the State Hospital is taking the issue of bullying seriously and is working with staff to make it clear that bullying is not acceptable.
"This government remains clear that we will not tolerate bullying of any kind in our NHS. It is not good for our hardworking NHS staff - particularly in an already challenging environment like the State Hospital - and it is not good for patients. The Minister will meet with the Board Chair and Chief Executive to discuss these figures and seek further clarity on what action is being taken."

Grant, 29, made 24 appearances for Vale this season, but moves to the ABAX Stadium on a two-and-a-half-year deal.
Striker Mackail-Smith, 32, has scored only five goals in 40 games for Luton since joining the club in August 2015.
He scored 99 goals in 212 games for Posh from 2007-2011, before returning for a one-month loan spell in 2014.
The Scotland international has made six appearances this season, with three of those coming in the EFL Trophy.
"Unfortunately we haven't seen the best of Craig due to his injuries, but with a prolonged run of games I'm sure he'll be an asset," Luton manager Nathan Jones said.
Posh chairman Darragh MacAnthony said on Twitter that Mackail-Smith had insisted that he would pay back his wages if he was not fit to play whilst on loan.
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The number of bullying claims by staff at Scotland's highest security psychiatric hospital is twice as high as previously reported, it has emerged.
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Peterborough have signed Port Vale midfielder Anthony Grant for a "six-figure fee" and Luton's Craig Mackail-Smith on loan to the end of the term.