Thank you for your answer !
I also think it may be leftovers but I wonder why it's only his belly scales that are flaking.

Actually his eyes never really cleared up, they've been cloudy for weeks. (the last picture was the first day I got him, so the eyes were not cloudy at that point)
Not blue and opaque but definitely cloudy and less clear than usual, with still the weird white outline around one of his eye.
I can clearly tell when I briefly inspect him under the flashlight of my phone.

Indeed after doing my research I was expecting him to shed once a month like your yearling !
How much time does your girl take to go through the whole process ?