Hello
I have a 2001 Mustang.
The Clear Coat on the TOP of the rear spoiler was really a mess.
Today, I almost got all the Clear Coat off with 600 gt sand paper.
I was going to follow this up with 1500 gt.
Spray paint.
Finally Clear coat.

My issue is this.
Right now all I have sanded was the top of the spoiler where the damage was. Not the underside where there is no damage. What I'm worried about is where the two meet? The new coat and the original coat, just under the rim or edge of the spoiler. Will they fuse together? I'm worried about the fusion of the two? Should I just sand the whole spoiler top and bottom?

Thank you all for all your help.