According to a summary of facts received by the Herald today, Sinclair has been working as an accountant in both New Zealand and the United Kingdom since 1970.
The IRD first began investigating him when they received information from various recruitment agencies indicating he hadn't returned contracting income he had earned for income tax or GST purposes.
He worked as an independent contractor between 2011 and 2016 and did not file any income tax or GST returns over those years.
All contracting was through recruitment agencies and involved providing accountancy services to Government departments and organisations, the summary said.
Those groups included the Ministry of Education, Wellington City Council, KiwiRail, the Department of Internal Affairs, and the then-Ministry of Foreign Affairs and Trade.
The total amount of evaded tax and GST was $170,852.89, but with penalties and interest the amount owing to IRD was $439,940.91.
The last contact IRD had with Sinclair was by phone in April 2011, and various means were used to try and contact him in the following years, with no luck.
In 2015 IRD tried to prompt contact with Sinclair by imposing $400 per week deductions on his bank account, but after the second deduction had been made, Sinclair transferred the rest of the money out of the account and closed it.
He received pension payments into another account, but began transferring or withdrawing the money as soon as it appeared in the account, meaning the deduction noticed couldn't be actioned.
Eventually IRD was able to retrieve about $60,000 after issuing a deduction notice to TSB Bank.
According to the summary, from 2010-2015 Sinclair made purchases in excess of $172,000 from various stamp and rare coin vendors.
His stamps were raised in court yesterday as assets he could auction off to pay back the money he owed to the Government.
But Judge Stephen Harrop was unimpressed, saying Sinclair, who pleaded guilty in August last year to two representative charges of tax evasion, had already had more than enough time to auction off the stamps.
"Why has he not taken steps to sell the assets he bought with the money he stole from the Government?" Judge Harrop questioned.
The reparation payment of $138,000 will instead come out of money owed to Sinclair from his cousin's will.
IRD has notices in place that will ensure the will money cannot be paid to Sinclair until the IRD has received its cut.
Sinclair was sentenced to six months of home detention, 150 hours of community work, and was ordered to pay the reparation once he received the money from his cousin's estate.