That depends upon your definition of Sati.
The source of the title is Maa Sati, who burned herself for hearing insult of her husband in front of her. This was out of pure love for her husband, Lord Shiva.
By Sati, we basically means a chaste woman. Every shastra praises a chaste woman.
As you already give references in the question, the first two references you give in the question, i.e., from Parashar Smriti and Agni Puran, here they talked about woman who loves her husband so dearly that can't live without him and burns herself with his funeral pile. Woman like this will go to heaven.
Now, talking about one from Mahanirvana tantra, here it may be about that woman, who by desiring of heaven, burns herself with her husband's funeral pile, she goes to hell. See again the verse, there is important word written there, 'Delusion'.
This 'Delusion' here refers to greed of going to heaven. She is not doing this because of her love for her husband but maybe because of other reasons. Other reasons can be many like just by being inspired from other woman or for wanting heaven or for brainwashed by someone to do so.
Such a woman goes to hell because it is committing suicide. Suicide is always mentioned in hinduism as sin.
While in first case, it is because of pure love for her husband. In that case, it means that she completely surrendered to her husband and wants to accompany him even after his death.
Surrendering completely whether to god, your parents, husband, is mentioned in shastras as giver of moksha.
In my opinion, ten million years in parashar smriti is symbolism for moksha.