UK License to Japanese License – How Is the 90-Day Rule Calculated?

I would like clarification regarding the 90-day residency requirement for converting a UK driver’s license to a Japanese driver’s license.

I understand that one of the requirements is that the applicant must have stayed in the UK for at least 90 days after obtaining the license. However, I am unsure how this 90-day period is calculated.

I am not a UK citizen. I studied in the UK and obtained my driver’s license there. I later moved to Japan for work and currently have no plans to return to the UK.

I passed my driving test on October 6 and remained in the UK until January 12, which means I stayed more than 90 days after passing the test. However, although I was legally allowed to drive from the date I passed (as indicated by the “valid from” date on my Uk license), the physical license was issued on November 8.

If the 90-day period is calculated from the issue date (November 8), then I stayed in the UK for fewer than 90 days. If it is calculated from the date I passed the driving test (October 6), then I meet the 90-day requirement.

Could anyone clarify:

1.  From which date is the 90-day period officially calculated — the test pass date (the “valid from” date), or the license issue date?

2.  Would I qualify to convert my UK license to a Japanese license without taking the full driving test in Japan?

3.  Is it possible to explain my situation to the Driver’s License Center and demonstrate that I legally held driving privileges for more than 90 days?

Any guidance or similar experiences would be greatly appreciated.