Topping up State Pension while living abroad

icasl

I worked overseas in the travel industry from 1987. The travel companies I worked for were based in the UK so I paid NI in UK until 2006. I then had my twin boys in Spain.  I returned to live in the UK in 2017. I note that I am not allowed to top up before 2006.To top up my NI one of the questions asked is what is the name of the company you last worked for in the UK? Is this 1987 or the tour operator before 2006? Any guidance would help please as the companies i worked for pre 1987 have long closed down.