Glass panel compability for iMac 21.5'' late-2012 (A1418 - EMC 2544) Do 21.5'' iMacs from other years use the same glass panel than the A1418 of late-2012 ?  

Not only the screen diagonal 21.5'' must be same, but also the height, width, thickness, and width of the black frame.
It would be to replace a broken panel, whilst the LCD is undamaged.
After several readings on the web, it seems that the late-2012 and 2013 model share the same panel. Mine was a LM215WF3 (SD)(D1) from LG.

The 2011 model uses another display. 

The 2012/2013 model use kind of monolithic display where you cannot replace only the glass independantly from the LCD.