`Your personal reference numbers` in Permanent residence app form

[chaoscontrol]

Hi everybody . Firstly I must say Thank you all on this great forum for explanations . all your advices are massive help for me .

I am flling Permanent residence application form : and there is something what I never seen before :

in Section 1 -
Applicant’s details :

1.22. Home Office reference number(s) :
Include any registration certificate or residence permit number(s)

and 1.23 UK national insurance number

anybody please explain what does that all mean ? do I need to find reference number on my 5 years residence document ? or somewhere else ? is this obligatory or I just need to put n/a ?

Thank you .

[alterhase58]

Check back to your previous paperwork and quote the reference number used there - expect this would take UKVI straight to the record they have for you. National Insurance is obvious - quote it!