New research on the number of New Zealand soldiers who served at Gallipoli in 1915 shows the figure is actually twice that implied in official war histories.
The research has been done by the Ministry for Culture and Heritage, and the New Zealand Defence Force.
It cross references digitalised First World War service records with unit movements and official war diaries.
It was found that military service files that recorded a soldier's career weren't concerned with placing them in a particular campaign or theatre of war.
That meant that in some cases, the Gallipoli box simply wasn't recorded.
The finding of meticulously kept notebooks this year, means the numbers could be calculated with higher accuracy.
Rather than the 8500 soldiers thought to have taken part, the number was actually more than 16,000.
MCH chief historian Neill Atkinson said the research, which began in November last year, was the most comprehensive investigation ever undertaken into the total numbers of New Zealand soldiers who served at Gallipoli.
"Thanks to Archives New Zealand's digitisation of First World War service records in 2014, the researchers were able to analyse thousands of individual military service files but soon discovered there were limitations to these types of records.
"First World War military service files recorded a soldier's military career, movements between units, and illnesses, but were less concerned with placing them in a particular campaign or theatre of war. Sometimes that 'Gallipoli box' simply wasn't checked," said Mr Atkinson.
Further analysis of unit movements and official war diaries gave a much better understanding of Gallipoli service, but NZDF historian John Crawford was certain there must have been other records maintained of unit strength, departure of casualties and arrival of reinforcements.
The major breakthrough came in January this year when Mr Crawford discovered the notebooks of the Deputy Assistant Adjutant General (DAAG) of the Australian and New Zealand Division in Archives New Zealand.
"These meticulously kept records detail the movements of Australian and New Zealand Division soldiers on and off the Peninsula during June, July and August 1915 and meant we could calculate the total numbers with a much higher accuracy," Mr Crawford said.
The research initially looked at 2429 service records of the 6th Reinforcements, the last reinforcement to reach Egypt before the end of the 1915 Gallipoli campaign. This analysis showed that at least 76 per cent of these men served at Gallipoli, but that military service records alone could not provide a definitive answer. The project expanded to cross-reference unit administrative files and to search for other relevant material, including the recently-rediscovered DAAG's notebooks.
The final figure was reached by adding the results of the 6th Reinforcement research, the numbers estimated to be present in April-May 1915, and the numbers from the DAAG's notebook research. The research methodology was overseen by Statistics New Zealand.
"This figure is by no means final but it's the most accurate we can achieve using the evidence we have discovered to date," said Mr Crawford.
Mr Atkinson said the project illustrated how knowledge about our history was constantly evolving as new information was discovered and new interpretations developed.
"The First World War centenary in particular has provided a valuable opportunity to review and re-evaluate research about New Zealand's involvement in the First World War."