Suse

Hi I’m living in Australia for over 30 years since 1986 I don’t have details of all my employment only really the last 20 years and not all dates just approximate. What can I do about missing details of employment. Also how do I find out if it’s worth paying for more credits as I only have 8 years. I have the list on how much I need to pay for each year so very confused but no other details.