Don’t have the Cassells book to hand but I suspect the Jeeps are stored and not withdrawn. This pic predates both the summer excursion season and of course the spoil work going at full blast, which effectively rescued the WTs from early oblivion (the oldest was only 18 years in ‘67). No Jeep was withdrawn until 1968, and at least one of the locos pictured was in service until 1970. The last three Jeeps were actually on NIR books until 1971 - 4, obviously enough, and 51/53. At the time this photo was taken in 67, some ex GN locos also remained on the books - including an SG3 and two UGs.