I slightly concur with the above. All dies are their own die pairs or varieties. The way I take it, errors are usually a one time occurance (or not corresponding to any other errors, and may be similar by coincidence), and varieties are anything that depicts the die. Die stages, are a variety. Die clashes (which are not a die stage imo) are a variety.
Die clashes are a variety of said die, if they happen. There will be a duration of coins struck while the die has the image, before an employee notices that the die has had been compromised. Therefore it is a die state of a singular die pairing. It is as struck.
I guess I am being just too technical. A die stage like a crack or a clash would in fact pump out coins mirroring that crack/clash, but that itself does not make it a "variety." How do you explain the difference between a hubbed doubled die and a die crack? Are those both varieties? One started that way before one coin was struck, while another occurred as a result of striking stresses on the die. The very point it becomes damaged from a crack, a clash, a shattered die, alterations from overpolishing to fix a problem, it then becomes a die stage. The 1955 doubled die is a variety, the 3 legged Buffalo nickel is a die stage. An overdate is a variety, a die crack is a die stage. A die clash was not hubbed that way, so it can't be a variety; it is a die stage. Many people, dealers, and even some reference books use them interchangeably, but there is a difference. Thus you need to ask yourself, "What caused this coin to look this way?" A variety does not simply mean a die flaw was transferred to struck coins. It matters when it occurred.
I thought we were all on the same page. A variety because it becomes different every time the coin strikes a die, Is the same as a die stage, only so few are recognized but they are one in the same.