Here's a fairly thorough thread on the topic...
My post on the topic needs an update...
Since that post I filed my 4x5 carrier (using the jeweler's saw). After sawing, I used pin files to "break" the sharp edges. Then I used steel wool to ensure the area in contact with film is absolutely smooth. I painted the edges with matt black model paint.
I didn't plan to reveal this publicly, but sometimes facts are important to illustrate a disputed concept. Though the borders can be faked, they can also be honest.
I dated the carrier after I cut it. A year later I made another very slight cut and marked the the carrier with the date of the cut. Anyone who inherits my equipment and prints will be able to verify vintage of any of my 4x5 prints by looking at the negative carrier. In the galleries "Dad and the twins, Laguna" shows the current cut, it's upper right near the trees. "Soccer Parade" is obviously older vintage. Though I could make more prints, I cannot fake that vintage.