The Journey To Excellence report assumes that you are using the recharter process to track who was included in each year's recharter.

This can be done by going to Membership → Recharter → Recharter Years as shown below.

Each recharter year is linked to the members who were registered with the troop at the beginning of that year.

Objective 3 of the Journey To Excellence report computes your retention rate based on the registered members at the beginning of the current charter year compared to the registered members at the beginning of the previous charter year.

If your unit's charter year ends on December 31:  You will compare the registered membership at the beginning of this calendar year to the registered membership at the beginning of the previous calendar year.  So, for example, if you are producing the 2019 Journey To Excellence report you will compare the registered members as of January 1, 2019, to the registered members as of January 1, 2018.  This is not a typo!  The BSA really does want you to calculate this objective based on the previous year's experience.

If your unit's charter year ends in any other month:  You will compare the registered membership as of the recharter that occurred within this calendar year to the registered membership from the previous recharter.  So, for example, if you are producing the 2019 Journey to Excellence report and your charter year ends May 31, you will compare the registered members as of June 1, 2019, to the registered members as of June 1, 2018.