Immigrationboards.com

Passport form require following

If both parents named below were born after 31st December 1982 OR were born outside the UK, we will also need the full name, town, country, date of birth and date of marriage of your grandparents (or details of your parents claim to British nationality). Write these details in Section 8, or on a separate piece of paper.

This means that if your parents are born outside UK you need to give me details of your grandparents, in case case my grandparents passed away ins 1940's and no detail in available what to do

Parents/grandparents' details are not relevant for passport applications based on applicant being naturalised as British.

I would agree that they are not relevant, but the passport application form doesn't agree. It clearly states you must provide the information.
Is there any documentation that confirms your opinion?

If you naturalise, then parents’/grandparents’ details are irrelevant for your British citizenship.

However, if HMPO ask, then do provide any available information. If you renew a lost passport in the future, then I suspect they may also ask again and compare the answers to prevent identity thief?

Keep a copy of your application for reference.