Julie gave one explanation. Another could be that it is the result of how
Project accounts for lag and lead times between subtasks or subtasks with
constraints. When it computes progress on summary tasks, it divides the sum
of the subtask actual durations by the sum of the subtask's total durations
to compute Summary % Complete. It then multiplies that by the Summary
Duration to get Summary Actual Duration, and then in turn subtracting that
from Summary Duration to get Summary Remaining Duration. Finally it
subtracts Remaining Duration from Summary Finish Date to get an effective
Worked Through date to use to draw the end of the summary's progress bar.
Because it's computed by subtraction from a future finish date, that
effective worked through date sometimes can land in the future, especially
if there are lag times still to come between some subtasks or SNET
constraints on subtasks that are still in the future. Remember the summary
metrics aren't "real" in the sense that they represent a measurement of
something tangible - they're simply the aggregate of subtask metrics that
are real measurements. They represent averages - the average family has 2.3
children but have you ever seen 1/3 of a child?
