Ten people died when the bus overturned on a roundabout on the A40 at Raglan in July 1995.
The victims said the delays are adding to their misery.
Many are still suffering flashbacks and nightmares and said their fight for justice is making it difficult for them to get on with their lives.
The day trip to Stratford-upon-Avon from a social services day care centre in Aberdare was planned as a special treat.
Many of the 42 passengers had mental health problems.
Pearl Griffiths suffered spine and rib fractures and lost the sight in one of her eyes.
She has been offered £35,000 pounds in compensation although a legal debate over the settlement is continuing.
A survivors support group meets twice a month to help them come to terms with the tragedy.
Pearl Williamson, the group's treasurer, was badly injured in the crash and has had five operations.
Desperate need for compensation
She has received her compensation settlement but says others are desperately in need of the money.
A spoksman for the insurance company CGU said they had settled the majority of cases.
The remaining claims would be resolved in due course.
Several months after the crash, coach owner Ronald Lewis was fined £750 after he admitted responsibility for the defective brakes and faulty speed limiter on the vehicle.