Like many, I've got numbers that don't really seem to add up. Mine states 23 years, need 11 more. Then lists out 23 years back to the first year I was in the UK, including the current tax year (so "no information yet"), two of which are gaps (as I expected). So actually that seems to mean 21 years including the current year. Whether I can trust that I only need 11 more, or actually 13, I've no idea. I don't know if you get credited for 16-18 on the basis that you were in education, if you weren't in the country and didn't yet have an NI number.
[my sister's got a saga on that topic - when she first applied to get an NI number they refused at her interview, saying she was lying that she didn't have one already, she must do as all UK citizens get them automatically. No, UK citizens not born in the UK don't ... Come to think of it, that will have knocked a few years off her contribution records I think]
I think that there was a point at which the years required for a full state pension was decreased to 30. And then when the system changed there must have been transitional arrangements that explain why so many of us seem to need something between 30 and 35 years.
I also don't understand the contracting out numbers. My forecast says I will get the full amount, but also acknowledges that I was contracted out for a time and gives an equivalent amount from that. I don't know if my final amount would be decreased by that? Clear as mud ...