You're welcome.....
.....but let's back up a bit. You tried to clean the butt cap and then white paint came off? That is really weird. The butt caps were made of white plastic and the logo painted red.
There were black butt caps used on Wilson frames back then, like on the Sting and more pertinently on the Wilson Ultra 2 that was also made in SV.
Seeing that the bumperguard and grommets were replaced (as they should be if they're worn out or if previous owners wanted a bumperguard put on), maybe the butt cap was replaced as well and painted to look like what should come on the PS85.
I saw that JoelDali commented in your other thread about there not being any red primer showing. He does have a point. Often you can see it at chips, but you can also see it on wear points around the PWS (from shanks) or at the drill holes for the grommets.
You brought up the possibility that sticker might be a replacement. Maybe.....as it looks like it's a paper sticker. The ones I'm familiar with were more of a vinyl or plastic type of sticker. Maybe it's just really worn.
Although the grommet channel ends are squared. That's totally a Chicago/SV feature.
I'll add your pics from the other thread here. Maybe even more pics would help.....