The Progression GDB
There are a multitude of ways to create the Progression Map and to store the required perimeters. No one way is right or required as long as the data and the resulting map follow GeoOps standards in naming, attribution, and structure.
However, following the best practices outlined here will allow for the greatest flexibility in the process and ease of data access and use.
Perimeters (the Fire Polygon) should be exported after every update, starting on day one. It is always easier to do immediately rather than searching through backups.
Saving them as feature classes to the Progression GDB preserves the Event Schema and allows for easily combining data.
Ensure the date and time are saved in the name (part of the GeoOps Standard) and the attributes (PolygonDateTime, a required-when-applicable field in the Event Schema). This way the perimeter date is easily found from any interface and preserved if/when data is combined.