Secret filming by the BBC's Panorama programme this month showed vulnerable residents being pinned down, slapped, doused in water and taunted.
An e-mail from the hospital manager last November said "five Safeguarding concerns" appeared to have arisen.
It is thought this may refer to concerns raised with the council's Safeguarding Vulnerable Adults panel.
The e-mail, sent by the manager to support workers and nurses and seen by the BBC, said patients had complained of ill treatment.
It said they had allegedly been teased, forced to swallow medication, threatened, restrained when it was not warranted, and called nicknames which other patients then used.
The e-mail read: "My worry is that these may be happening and some of you do not feel comfortable to challenge what you see.
"I have always said (you have it now again in black and white) I do not condone ANY practice that is less than bespoke for this type of service."
"Safeguarding concerns" would normally refer to matters referred to the Safeguarding Vulnerable Adults panel at the local authority - South Gloucestershire Council.
The leader of the council's Labour group, Councillor Andy Perkins, told the BBC he was really surprised he had not been told about any concerns when he presided over the social services committee last November.
The private home, which is taxpayer-funded, is to be investigated by the Care Quality Commission.
On Wednesday, Labour health spokeswoman Baroness Thornton added her voice to calls for a public inquiry into the alleged abuse.
Speaking in the House of Lords during an urgent question on the subject, she told peers she wanted a wide-ranging, independent review to "shine a light" on events and allow lessons to be learned.
Police this week arrested two women, aged 22 and 21, and three men, aged 58, 40 and 28. Last week, a woman and three men were arrested and all nine have been released on police bail.
Hospital owner Castlebeck has apologised and suspended 13 employees - including the manager who wrote the e-mail.
The patients filmed by Panorama have been moved to safety.
Council staff may have been been told five times in two months about fears of abuse at Winterbourne View hospital.