Thomasina Bennett, from Belper, had Alzheimer's Disease and was staying at Milford House Care Home in April 2012.
Derby Crown Court heard there were no industry-wide regulations on the fastening of wardrobes to walls in care homes.
Milford House Partnership denies two health and safety at work charges.
A jury was also told personal activity monitors - used in Mrs Bennett's room and elsewhere in the care home - were "systematically unsafe".
Mrs Bennett's daughter previously told the court her mother's monitor had not gone off before she was found.
Giving evidence for the defence, group business manager Pierre Falleth added no regulations existed for the use of such monitors for residents at risk if they got out of bed.
"It was awful what happened, but we could not foresee it," Mr Falleth said.
He told the court he warned other care providers after the accident, contacting them as chairman of the Derbyshire Care Providers Association.
He said: "What happened was incredibly awful. A lot of people were extremely distressed by it and we didn't want it to happen to anybody else."
At a meeting of care providers, Mr Falleth said he spoke to national providers as well as smaller groups.
"I can tell you that nobody had secured wardrobes and none of them had come across this before," Mr Falleth said.
After Mrs Bennett's death, Milford House Partnership fastened all wardrobes to walls and introduced checks on personal activity monitors.
Gerald Hudson, 72, from Ambergate, trading as Milford House Partnership, which runs three care homes, denies both charges brought under the Health and Safety Act.
He does not have to appear in the dock or attend court as the charges are brought against the partnership.
The trial continues.
A care home manager has told a court he could not have foreseen an accident which led to the death of an elderly woman who was found under a wardrobe.