In cases where the permit does not include everything you have done, for instance you had a siding permit and you also finished the basement when the work was being done, the Assessor must address all of the changes during the inspection. The Assessor must value the entire property each time it is re-assessed.
Not getting a permit for work done in your home does not prevent an assessment. It is also unwise to have work done without a permit for two reasons: 1) building inspections are necessary for safety, not a method for raising revenue for the Township. If your house had a fire and sustained damage, and you did not get the proper permits and inspections, your insurance company might not reimburse you for damage, and 2) if the Assessor's office discovers that you have done something to improve your property value, an assessment is made regardless of whether there was a permit or not. The Assessor will then have to assume that the work had been done within the past two years and issue assessments for both the current and the past year.