The sentence "they were collected" is correct and can be used in written English.
For example: All of the books were collected from the shelves and donated to the library.
(They were collected at the end).
By the time they were collected, erosion was far advanced.
After all, they were collected at considerable taxpayer expense.
"They were collected as part of the historical record," he said.
They were collected over the decades by his wife, the feminist playwright Suzanne Spunner.
His programme notes were so good that they were collected into fat, richly informative volumes.
"They were collected originally as ethnographic objects of a culture that was meant to die out.
They were collected by a coastguard vessel and taken to Kanazawa for questioning.
Second, there were the scattered pieces of human remains; they were collected and are now being studied at the Smithsonian.
All but one of the fragments has remained frozen since they were collected, Dr. Brown's team reported.
