I’m hardly the expert in this stuff but long ago I did wonder the same thing on my own 34k mile original paint GN. What I found was this particular area looked suspect on many low mile, factory paint, examples I looked at (good ole 80's GM manufacturing at its finest). Many had filler in that seam. Just for fun I went to the Bring a Trailer website because they post lots of photos. I have attached photos from a 17,000 mile GN; 1,200 mile GNX; 296 mile GNX, and a 55 mile GNX respectively for comparison (sorry for the poor quality photos, I just took a pic of my screen cuz it was faster that way) but you can go to the site if you want to see the pics clearer. Bottom line, yours looks on par or better than some in the photos. My guess is yours is likely how it came from the factory (except for the hole that was punched to apply undercoating). Hope this helps.
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