There could be a payment problem with free NHS care if the questions are ever asked.
Some branches of the UK medical profession today appear to be more "required" to ask about eligibility for NHS free care as an SOP.
After a recent heart attack the UK hospital to which I was blue lighted the
accounts people certainly asked me.
After my treatment.... I was required to convince them of my eligibility to free care.... via time resident and recent tax returns...I think it was to complete their paper work.
In the case of long term expats. returning and seeking NHS free care,the period to complete one tax year and send off their tax return could be important....it seems wise to have private medical insurance cover for this period.
The Class 3 NI contributions by an expat. non resident in the UK.
Only "Protects their yearly contributions" to their UK State pension.
Apparently these Class three contributions and have nothing at all to do with eligibility for the NHS free care.
I could be totally wrong on all of the above but I am comforted that you have found the bottle of "Something Nice" system also works wonders.
Possibly what you say is correct for Scotland and what I say is correct for England.
Anyway according to the Daily Mail the best way to return to the UK seems to be as a political refugee seeking asylum and that way you could also get a free house and live on benefits and also save on buying the bottle.
Cheers.