Edexcel has apologised, and three students have had their grades upped from a "C" to a "B".
Some had been holding conditional offers from universities, and one almost lost a place because of the mix-up.
Last August, 15 students taking A-level music technology found that their results came out later than the rest, and some grades were lower than expected.
Nigel Robbins, principal of Cirencester, took it up with Edexcel. At first the board denied losing the work, which should have counted for 40 per cent of the final mark, he said.
"The apology, when it came, was late and grudging. But the real issue was that they had awarded grades on the written papers alone," he said.
"They ignored the college's previous estimates of candidates' likely grades." He lodged an appeal with Edexcel but says he had no response, despite a protest from Cotswold MP Geoffrey
"I had to ring again," said Mr Robbins. "They said that they were waiting for us to send in copies of the coursework."
The lost work had consisted of tapedrecordings and there were no copies. The college hastily gathered other pieces of students' work and sent those in.
But Edexcel insisted that the work would not have secured better grades. Cirencester College protested again. Now Edexcel has done a U-turn and upgraded three students.
One of them, 18-year-old Stephen Banks, almost lost his place on a degree course in jazz studies at Leeds College of Music.
His mother, Barbara, said: "It took them a very long time to acknowledge the fact that they had lost the coursework, and it took them even longer to do anything about it.
"I think their whole reaction to the situation has been really appalling."
Principal Nigel Robbins said: "We are in the age of customer relations and I just think they should have given this particular problem a much higher profile from the very beginning.
"I have never had any comment from the chief executive of Edexcel although I did write personally to her."
A statement from Edexcel said that it had apologised to Cirencester College.
"Edexcel deals with over two and a half million scripts each summer and, fortunately, very few packets of examination work are permanently lost in transit."