The classification concept where non-classified pieces of information together render a new document classified is known as:

The concept where non-classified pieces of information come together to create a new document that is classified is described as "Classification by Compilation." This principle illustrates how combining various unclassified elements can lead to the creation of classified material if the cumulative information reveals sensitive or classified insights that were not apparent from the individual components.

Classification by Compilation emphasizes the importance of understanding not just the individual classifications of pieces of information, but also how their combination can lead to a new classification status. This is particularly crucial for ensuring that sensitive information remains protected, as it highlights the need to assess the implications of compiling various data sets together.

In this context, the other options do not accurately capture this specific mechanism; they address different concepts related to classification but do not specifically denote the action of forming a classified document from non-classified elements through compilation.