you have to reference the 4604(d)3 and have a clerk, manager or regional office that is either familiar with it or will look it up. Many times they are not familiar with it and try to tell you it has to have been already registered as such with the antique plate. Not true. This is becoming more difficult as the old timers in the DMV system have retired and interpret it differently. Bottom line is if it is 25 years old or older, of historic significance and you qualify as a collector as described in their statue, you should qualify for the exemption.
I too have never had to pay back penalties due to this but am finding it more and more difficult to relay the same level of understanding of the applicable statutes to hobbyists and especially more difficult to find DMV personnel that are willing to see it the same way.