HI Sabbu161,
i agree with you on this. MPNP may be OK with secondary education documents to show date of birth; however, if you research online, you will find that CIC is very particular about the birth certificate document. Therefore, I have suggested to get a non-availability certificate and other documents as mentioned in my post.
If you find any example of a person, who has submitted to CIC (main application to CIC after nomination is obtained) secondary certificates only for date of birth, and CIC has accepted it successfully, please let me know. I will be happy also because my relative is also applying for MPNP and she does not have birth certificate either.