Advise on completing K15 form

I bought my house new in 1976 on an estate from a developer and would like to register it for the first time. I understand I need to Submit a K15 form for a search as the first step in process to getting it registered. Do I just put the developer on the request for a search or do I need to try and identify the people he bought the land from many years before?

Ernest - please refer to our PG 1 sections 4.3.12.2 and 3 and the linked section 4.4.5 -&#160;<a href="https://www.gov.uk/government/publications/first-registrations">First registrations (PG1) - GOV.UK</a><br> LCs against your seller at the time are required