I have Hagerty insurance too on my Mustang and my Dart.
When I first got the Mustang insured about 4 years ago I had to get an appraisal but when the Dart was added two years ago I did not have to get an appraisal and we had an agreed value of $15K for the Dart. All they wanted was detailed pictures.
The Mustang was originally appraised for $13.5K.