I suspect you shouldn't have been able to do that even then Cal. I have spent the past 18 years in the Czech Republic, six months at a time. As a pensioner I can be out of the UK for six months, but no longer, without losing my right to NHS treatment.
Non-pensioners are only allowed 3 months. This is despite being UK tax resident, drawing a UK pension, and having my permanent abode in the UK. I have always been very careful to keep within those limits though until fairly recently I am not at all sure there was any way that they were checking, other than asking me every so often.
What always annoyed me was that they would not commit themselves on whether you counted within a tax year or a calendar year.
As far as I remember, these rules have been in existence since I started to live over there, so for at least 18 years, if not more.
You were probably quite lucky!
I have a vague memory of there having been some rule about residence for at least 6 months in your first 5 years prior to going overseas. But I might be totally wrong. I know some friends, whose children were not born in the UK, did not qualify, but I think the parents did.
However, I'm very grateful that I was granted this, for whatever reason. Even if it was only because my doctor knew I was working for a charity.