Hi Andy,
When tracking in Project, I (and I believe others here) do not recommend
using only % complete. I suggest using % complete as well as updating (as
necessary) the Remaining Duration field (available on the Tracking Table.)
If you have placed a constraint (Finish No Later Than) on a task and that
task violate the FNLT than constraint because of tracking, the Planning
Wizard will appear warning that a scheduling conflict will occur due to the
constraint. (This assumes the Planning Wizard is enabled on the General Tab
of the Tools >Options dialog box.)
Hope this helps. Let us know how you get along.
Julie