In what cases may component "Tempering" be required prior to assembly?
This is determined by the Moisture Sensitivity level of the component. If a component has been in an uncontrolled (as defined by the MSL requirement) longer than it is permitted prior to reflow, it needs to be baked to ensure all the moisture (well, the vast majority of it) has been removed to prevent popcorning.

Even passive components have this stated in the datasheet, such as the one below:



Note that MSL varies depending on process; I have seen the MSL for a component be 4 for a leaded process (peak reflow temperature 220C typically) and 3 for a lead free process (peak temperature 245C to 250C).

I must admit 2 weeks seems excessive, although I have seen a programme using a low temperature bake for many days due to other issues with the parts.