Please cite an authority that teaches the concept of a so-called natural justification.
There is no "authority", but it's speculation ... just as BoD is also 100% sheer speculation without any foudnation in Public Revelation.
Similarly ... take Limbo. Limbo actually involves taking the distinction between the temporal punishment due to actual sin and the supernatural deprevation of sanctifying grace which can be due to Original Sin alone. This is an extension of the same notion, where just as infants who die unbaptized do not die in enmity with God, but in fact remain in a state of natural friendship with Him, and therefore enjoy a natural happiness, a concept of a natural justification would be something akin to approaching this state of natural non-enmity with God. While natural virtue and good will can put one in such a state, it doesn't suffice for entery into the Kingdom, i.e into the supernatural life of the Holy Trinity.
AND ... Limbo is as much sheer speculation as anythign else. While it's not mandatory, and the stricter opinion of St. Augustine may be held, no less authority than St. Thomas gave it the full weight of his authority, and the Church condemned its rejection as a "Pelagian fable" (aka speculation rooted in implicit Pelagian heresy).
If there's one area about which God has chosen to reveal so very little, it's the detailed explanation of who goes where and in what state afer we die. God of course revealed about Heaven or Hell, but there was no revelation regarding Limbo, and yet the Church does not condemn it, and St. Thomas strongly endorsed the notion.
This "natural justification" concept is akin to that.