At the moment the fields "Number of records", "Number of staging records" and "Number of target records" only contain the number of last executed records on a job run.

For instance, when you import 20.000 record and 3 records fail to import to target. The number of records on the Job Runs table will show 20.000, but if you go to the staging data afterwards and copy the errored records to target the number of records on the Job Runs table will show 3.