The most reliable way to tell whether a job is finished is to check for whether or not the job has the status of Done.
If it does not, the progress bar will look like this:
If it does not then the job is likely not complete, but in very rare cases the status bar will seem to continue working forever, but will not process any more items. In this case it is okay to go ahead and click download.
If there are items missing in these cases please contact ScanPower support.