NVC Civil Docs - Marriage Certificate is not available

[SaiGrace]

I am putting together civil docs for my mother. One of the required document is her Marriage certificate. My mother was married in 1956 but does not have a marriage certificate. My father died in year 2000. Would my father's death certificate be enough? Thanks.

[moon47usaco]

What country?

There must be some way to verify marriage with the local government even if it was so long ago.

Does the death certificate list her as wife?