Virachai Plasai, head of the Thai team and Thai ambassador to The Hague, said the team noticed Cambodia's use of the falsified map as part of its formal request for the ICJ's interpretation in 2011 and had corrected it in Thailand's first written defence.
But the falsified map with "colourful adjustments" was used again by Cambodia in its second written statement to the court in March 2012, the Thai legal team head said.
Alina Miron, a map expert who is one of four foreign lawyers on the Thai team, said the Foreign Ministry found out about the falsified map a year and a half ago.
"I was very excited to see that map and we had to build up the story. Foreign Ministry staff have been really great in trying to find out the answers.
"They were wonderful trying to build the story up [in court]. Nobody wanted to do it but I had to," she said.
"I am proud to be helping Thailand. I have participated in this case because the Foreign Ministry contacted Alain Pellet, who invited me to join the team," Ms Miron added.
Thailand's team of lawyers in the Preah Vihear case met Prime Minister Yingluck Shinawatra at Government House Monday to report on their performance during the oral statements at the ICJ.
Ms Yingluck thanked the team for its hard work and research in Thailand's defence.
She also said the Thai people had given moral support to the team, and were proud of them.
Ms Yingluck said the team was able to clearly explain points of concern to the public and rebutted Cambodia's arguments.
The public were provided with information which made them more knowledgeable about the case and they had become more confident in understanding the situation after hearing the Thai legal team's explanations, she said
James Crawford, a lawyer on the team, said the Thai team had done a very good job and it is satisfied with its performance.
"[But] it's difficult to say how the court will rule after this. It's like being in the middle of the sea, like being in the hands of the gods," he said.
Mr Virachai thanked the government, officials from related ministries, and the Thai public who gave support to the team throughout their verbal testimony last week in the Hague, which he said showed unity within the country.
"One thing I want to mention to is the case of Prince Damrong Rajanupab who went to the Preah Vihear temple a long time ago as an archaeologist but his case was considered by the 1962 court, so this time we mentioned him to compare with the visit of then Prince Norodom Sihanouk of Cambodia which is a good legal point," Mr Virachai said.
Thailand has prepared detailed geographic coordinates as requested by one of the ICJ judges and will submit them to the court before the Friday deadline. He declined to elaborate on the details.
The ambassador said the next step is to continue providing information to the public about the final court decision by highlighting the critical points the team made during its oral testimony.
Defence Minister Sukumpol Suwanatat said that Thailand's coordinates would be based on the Thai cabinet resolution of 1962.
In a Defence Council meeting Monday, ACM Sukumpol thanked officers for preparing useful information, especially data on maps, for the Thai legal team.
Defence spokesman Col Thanathip Sawangsaeng quoted the minister as saying that useful information on maps had been very important for Thailand's defence in its oral statements before the ICJ last week.
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