There's no way to get the incompletes back to their previous state. The complete preferences will become corrupted if one of these happens: 1. The computer crashed. 2. You don't close LW properly before shutting down computer. or 3. You go back to an earlier version of LW.
The way to restart them is go to Library window, select incomplete folder, select the incompletes & press resume or right-click & choose force resume. But yes, they'll start form zero percent.