When selecting a date range for a report, you also need to consider your job status filters.
When selecting a report with a chosen date range, the date range is based on the planned start time of the job, or the actual start time if the job has been started.
Also, vWork has to take into account that there are some job status types that may not have planned start times one the job. (for example: unassigned, or cancelled jobs may not have a start time).
If your report filters include all job statuses which is the default report setting, then you quite often can get many more jobs than you expect...
A good rule to follow is to start with only reporting on completed jobs, as these will always have a start time.
Of course, if you are looking for data on a specific state like started jobs, this should work as normal.