Info regarding the sclerotic round density.
The other bit about the subluxation means that the acromioclavicular ligaments may be lax, and therefore your AC joint is unstable. There are different grades of laxity. When ligaments become "lax" at the enthesis, popping sounds are usually heard. These may get progressively worse as time goes by and are generally referred to as "overuse injuries".
To be honest even if it is a subluxation, the ligament signaling may appear to be completely normal on MRI, it's better seen on Ultrasound but even then it's easy to overlook things.
Either way, you can do a bit of palpitation where the clavicle and the acromion process meet and if it's tender that's a sure sign that there's an issue there. Although there may be no tenderness at all, which would be a good thing.
The MRI should tell you more either way. Let us know what you find out, and how your Dr plans to handle it. All the best.