Be sure to keep track of the small magnet along the left side of the display. It may be stuck to the LCD frames or to the rear display bezel.

When the display lid is closed, this magnet comes in proximity to a sensor on a small circuit board at the bottom end of the I/O board, to tell the Macbook that the display has been closed, so that the Macbook can go into clamshell sleep mode.

To reinstall this magnet, press it back into its cavity in the rear display bezel, with its short side facing up (see photo 2), then place the LCD panel back into the rear display bezel and screw it down so that the magnet doesn't drop out and disappear.