Neck Shims

I’m still fiddling with the set up on my HH it’s definitely acceptable but not spot on so keep going.
I went to alter it the other day and never noticed the signature and date, thought it was interesting so took a quick snap.
The question is more I also never noticed the dull patch on it, like there has been a sticker or more importantly a factory fitted shim but not in the traditional place.
Have any of you ever seen that or done that ?
In theory it might just work, rather than putting a shim at the heal, putting it elsewhere in the neck pocket for another effect?