Corn Snake with strange Scale on the top of his head

Hello, I actually made an account just to ask for some advice.

For a few sheds now I have noticed that my corn snake has a dark spot on his head that looks like layers scales that where not shedded properly. I am not sure when he started developing this, but he did have some shedding issues when he was a baby and perhaps this has accumulated for about 4 years since then .

I attached some pictures of him to see what you guys think, I tried rubbing it to see if maybe it was a loose scale, with no luck. Bear in mind that he is in the middle of a shed atm so he looks a bit grey.

I appreciate any feedback or information

https://www.dropbox.com/sh/6mmhz8tut...5N_Bslesa?dl=0