When an update is done via CSV import of leads, the count of the leads in the CSV file would not match with the count in the UI when the import label is applied in the filter condition.
Reason: This difference in the count is because the customer would have duplicate leads which were also updated during the import. For example, there might be more than one lead with the name "Lead A" and while updating, all the corresponding leads were updated. So, on the import history page, it is considered as a single record as the CSV imported has only one match to it. However, in the filters, all records are shown as they were updated as part of that import.