My parents are buried in the same cemetery in adjacent plots. I know where they are buried because I was there the day it happened. I am a source for that information.
Their death certificates are not.
Their death certificates give a date of burial, but the place of burial is only as specific as the township. They do not provide the name of the cemetery. So if I’m creating a citation to a record or reason as to how I know they are buried in the cemetery where they are buried, I cannot use the death certificate. I can use my knowledge. I can use the tombstone (even though we all know that tombstones are not always 100% evidence someone is buried in a cemetery). I can use the obituary which also provides that information. Not all these sources are always equally reliable. But they do state the name of the cemetery specifically and so I could cite them because that is what they say.
But the death certificate cannot be used as a source for the specific place of burial. In this case, it can only be used to source the township of burial and not the cemetery.
If a record does not state something, do not cite it for that statement.