Dear future self;
One day when you go to take Pembroke out, the north section can be removed with just the screws into the wall and the cabinets. They’re all accessible from beneath. All except this one screw at the end of the Pembroke Milling Company siding, which goes straight into the windowsill. You’ll probably find it completely buried in ballast.
The southern section has three screws into the windowsill. They are already disappearing into layers of primer and paint, but you can see there is a screw on either side of the track as it enters the layout. The third screw is almost in line with the end of the Lee Manufacturing siding one about 3/4 of the way along to the side of the window.
Good luck digging them out.
Your present self