Seeding your progression means to ensure that the very first activity in your progression has the proper fitness signature assigned such that your entire progression history can be compared and evaluated against other parts of your progression.
To properly seed your progression, go to the Activity Details of your very first activity in your activity history and use the Advanced tab to determine/enter the Fitness Signature that applied to this activity.  Use the Save/Lock button on the bottom right to save this signature to the activity.   Xert will then perform a trickle-down process from this first activity and adjust/calculate your progression information activity by activity.
Once the trickle-down completes, your progression chart should be a better reflection of your entire progression history.