Mr Rankin said old boys had served in the armed forces of New Zealand, Australia, Great Britain, Canada and South Africa and in all branches of the services from the Naval Volunteer Reserve, the Royal Medical Corps through to the Royal Flying Corps.
"All identified and recorded in detail... except for one," he said.
And that missing part of the great 'old boys who served' file is a chap by the name of Lieutenant John Snodgrass who ended up serving with the 7th Gurkhas.
While there is background about him from his school years and entrance to the military, his ultimate fate has never been uncovered, although there were reports he had been wounded at some stage.
John Snodgrass entered Napier Boys' High School in May 1907 and his father was the manager of the Bank of New Zealand in Napier.
He was a fine young sportsman - excelling in swimming, running and rugby.
He had also been in the school cadets, so his joining the Territorials in 1911 along with former classmates Leslie McLernon and Ernest Harston was no great surprise.
But he lost touch with them when he was transferred out of Napier (he had taken up work at the South British Insurance Company).
He went to the Auckland office, and it was later reported he had been transferred to Calcutta.
Young Snodgrass kept in touch with his old school however, and would write letters updating what he had been up to, and in 1915 he wrote that he had joined the 7th Gurkhas in Calcutta.
"Then all is silence," Mr Rankin said, although the word "wounded" was added to an official list of those serving in 1916.
"Did he serve with the Gurkhas on Gallipoli? They made a significant but often overlooked contribution to that campaign," Mr Rankin pondered.
"And was it there he was wounded?"
His former schoolmates had paid dearly during that campaign with 19 dying on the Gallipoli Peninsular as a result of wounds and sickness.
Mr Rankin said if Lieutenant Snodgrass had been wounded at Gallipoli he could, like many others in that situation, have been sent off to recuperate and then on to another battlefront.
"But all our attempts to find further information have failed."
There are no Gurkha records online and two years ago when two Gurkhas attended the school's Anzac Service they promised to pass on Mr Rankins' request for information to authorities back there.
"But a few days later Nepal was devastated by an earthquake which obviously set other priorities."
Mr Rankin said one thing they could be fairly certain about was that John Snodgrass did not return to New Zealand as a search of census records for 1920 came up only with his brother Bryan Clayton Snodgrass who had also attended Napier Boys'.
That was where the trail went cold.
"If he continued to serve after 1916 and then fell on some European or Middle Eastern battlefield he should take his place on our roll of honour," Mr Rankin said, adding had he survived they should have a fuller profile on him.
"Our lost old boy."