I was never able to successfully remove an emulsion without it tearing unless I removed a little of each edge. In my experiments the emulsion would eventually seperate in the middle of the neg but stay adhered on the edge or fray. The older the film the more likely it was to fray. The younger the film, the more likely is was to stay adhered.

The older the film the more likely it was to fray as it separated itself from the base. If you run your fingers along the edge of some older film (circa 1940s) the edges are pretty rough. This was very common with nitro negs. Scoring or cutting gave a clean smooth edge that did not fray.

Younger films needed to be cut because whatever was adhering the film to the edge to stop it from separating did not dissolve in water.