I have two WI collector plates. Each collector plate required proof of registration of another vehicle in the household with regular plates before they would be issued.

First car:
In 2008 the state required photos of my '71 Challenger to verify it was stock and not modified along with the application. I received a reply in the mail from the DMV saying it was rejected for being "modified" and hobbyist plates were being issued in 2 weeks unless I contest. With the exception of headers and MP valve covers, my '71 Challenger is stock restored including Polyglas tires.

I called the DMV in Madison and was able to get connected to the department that processes the applications. The DMV retrieved my application and the photos I submitted and said it was rejected due to the air scoop coming through the hood. I proceeded to explain to them what a shaker hood is. Then, I asked what do you use for research? Google? There was a pause, and they quietly say "yes". So, I told them to Google "71 challenger shaker". They reply "oh, you're approved". Got my collector plates a couple days later.

Second car:
I picked up a '71 Barracuda in 2020 sporting side pipes (since removed), which would disqualify it per WI DMV rules. Send in the application for collector plates and no photos. They changed the application to saying they may request photos. I was approved no questions asked. I'm guessing with the limited resources because of Covid they were just rubber-stamping approvals.