I think he is asking about the Razor Geometry

Basically the average angle of a SR edge is 16° if the razor has been abused like so many of the older Sheffields have been then the spine gets worn down un-equally to the edge and the angle drops enough that the Bevel first gets much larger then eventually the edge will fail because the steel cannot handle the lower angle...

As long as the edge and spine stay in sync then there is no issue, the angle can also go up or down from the factory set, how much depends on the steel...

If you are asking for an exact number of degrees that the angle can change before the edge fails the answer is the ambiguous YMMV