So about 3 years ago I decided to just live with the multiple cracks in the glass of my late 2012 iMac. The fact is that the glass and the LCD are one piece and not designed to be replaced separately
But it is also true that you can manage to remove the glass only and for a while there were a couple of examples of someone doing so on You Tube
Also about 4 years ago when I did my initial research you could in fact buy an aftermarket replacement glass for a late 2012 iMac. That product sat in my save for later file until eventually Amazon sent notice that the product was no longer available and it was removed
In my recent searches I can not find that replacement glass or any like it and for the life of me I cannot remember the seller
So it appears that parts of what everyone has posted is correct in some manner with the exception of someone being an idiot
The facts are the glass and the LCD are sold as one piece
Someone can carefully separate the glass from the LCD successfully
It appears that a glass only replacement for the late 2012 iMac is unattainable at this time
If anyone actually finds a replacement glass that works I would like to know as well