When does the nullifier "whoever doubts the disbelief of a disbeliever is a disbeliever" apply to a specific disbeliever, and when does it apply to the general category of disbelief?

Scholars have stated that not declaring polytheists as disbelievers, or doubting their disbelief, or validating their religion, is an act of disbelief itself. This refers to those who do not declare the known disbelievers, such as Jews and Christians, as such. As for a Muslim who commits an act of disbelief out of ignorance or misconception, and upon whom the proof has not been established, it is not permissible to declare him a disbeliever. Rather, his act is considered disbelief without declaring him a disbeliever, unless the conditions for declaring someone a disbeliever are met and the impediments are removed. As for the non-Muslim, in this world, he is treated as a disbeliever, but in the hereafter, his matter is with Allah, for Allah does not punish anyone until the proof has been established against them. Allah's actions are subject to His wisdom, and He only punishes those who turn away from the proof or stubbornly reject it after it has been established.