Around 1985, the stone was removed from the level pasture where it had stood and interred in a nearby quarry, ending its visible existence entirely. It is the kind of loss that tends to happen quietly, without ceremony, and is noted only in passing by the records that come after.

The stone was not entirely undocumented before it disappeared. A local historian and antiquarian named Grove White recorded it sometime between 1905 and 1925, noting its dimensions as approximately five feet six inches in height by three feet two inches wide, and even included a photograph. By the time the Ordnance Survey revised its six-inch mapping in 1938, the stone appeared on the map, positioned roughly 45 metres to the north-east of a neighbouring standing stone in the same townland. Curiously, it had not featured on the equivalent 1842 survey at all, which raises the possibility that it was simply missed by earlier surveyors rather than erected in the intervening century. A researcher named Bowman, writing in 1934, suggested that the two Knockduff stones may have formed part of a stone row, a type of prehistoric monument in which two or more upright stones are set in a deliberate linear arrangement. If that interpretation is correct, the buried stone was not an isolated marker but one half of a paired or extended alignment whose full meaning is now doubly obscured, first by time, and then by a quarry.