Evidence for Residency Test - Parent under 3(2) MN1

[CricketPlayer]

Hi there - great website.

My situation is as follows:
- My Father (deceased) was born in the UK, I was born in Australia.
- I have UK citizenship by descent.
- I have two children born and living in Australia (2 & 4 y.o., never entered UK), want to get them registered so they may enjoy citizenship.
- I understand they don't automatically get citizenship as they are twice removed from the grandfather.
- I understand under section 3(2), using form MN1, I can apply to have them registered so they may get their own UK passports.
- This would only be possible if I lived in the UK for a period of 3 years with no more than 270 days of absence - which I believe I meet.

I am curious whether anyone has experience with what evidence is required to prove the 3 year/270 day test. My time in the UK was in the mid-1990's and I have very scant evidence of my time there. I have an old passport which shows some coming and goings from other countries, but there are no UK stamps in the passport. I also have some old job references that showed I worked somewhere but that is probably about it - maybe some photos too.

If anyone knows what sort of evidence would typically be required to prove my time in the UK, it would be great. I.e. are they very strict or lenient?

Jeff