The "Next Service" & "Last Service" dates are a legacy feature that has been updated to the 5, 6, and 12-year fields. Originally, these fields were where customers used to record when 5, 6, and/or 12 year work was due.
The Next Service Date and Last Service Date fields are used by users differently - some use them to keep track of each inspection and next inspection, some people use them for service work, and others do not use them at all.
These fields do not generate on the inspection report, so users (if using these fields) use these fields to capture information internally. In the end, these fields are manually set and edited.