In 1663 at the Archbishop of Canterbury's residence, Lambeth Palace, a Gothic hammerbeam roof was built to replace that destroyed when the building was sacked during the English Civil War. Also in the late 17th century, some discrete Gothic details appeared on new construction at Oxford University and Cambridge University, notably on Tom Tower at Christ Church, Oxford, by Christopher Wren. It is not easy to decide whether these instances were Gothic survival or early appearances of Gothic revival.
In what century were distinct Gothic details used on new construction at Oxford and Cambridge? (If the question is unanswerable, say "unanswerable")
the late 17th century