Re class 2 or 3 NI, how long is immediate in "you worked in the UK immediately before leaving"

To be eligible for class 2 NI top up payments from abroad I understand that the condition is that "you worked in the UK immediately before leaving". In my case I had been working in the UK for 15 years prior to deciding to leave. I stopped work and then went back and forth to Ireland to look for and work and interview for various jobs. This took about four months before I secured a job offer and moved completely, during which time I was not employed or claiming benefit as I was married and my wife worked. I was then employed or self employed continuously for the next 30 years in Ireland. My question is, how long is "immediately" before leaving? Must you have stopped work the week before departing, a few weeks, within the same calendar or tax year? If it is absolutely just one week, I guess that year be class 3 but what of subsequent years? As it stands I have been told Imay pay top up NI from 2006 onwards, which is a decade after moving.

Hi Michael,
If you could complete and return our CF83 application form, after you have read leaflet NI38, then our International Teams will be able to check your entitlement to pay the voluntary class 2 National Insurance contributions.
You may find the NI38 here:
Social Security abroad: NI38
Before applying to pay voluntary contributions, may I ask that you first obtain a State Pension Forecast which will detail your current and future entitlement to a UK State Pension.
You may obtain this here:
Check your State Pension forecast
Thank you.