Next to the Grid is a zone called the Archive, represented by the Archive card. 

When you reset the Grid only 16 modifiers are placed in the Grid. Any remaining modifiers are archived (placed in the Archive). 

Modifiers in the Archive cannot be revealed.

Clarifications:

• When an effect tells you to archive modifiers, you place them into the Archive.
• Any number of modifiers can be in the Archive.
• The Archive is a zone. All modifiers in this zone are in play.