Hi Alone,
I assume you split the tasks through tracking and using the Tools > Tracking
Update Project, Reschedule uncompleted work to start after: command. If
you split the tasks in some other way, do let us know.
That will split tasks moving the incomplete portion of the task to the date
specified in the Update Project command.
You may manually "re-join" split tasks by dragging the split portion on the
right back into the left portion.
Another option if you have split many tasks by the Update Project command is
to use the Reschedule uncompleted work to start after command again, but
change the date to the last tracking you have applied.
I hope this helps. Let us know how you get along.
Julie