I’m sure that diamond stones (actually plates) are shipped “as plated” because any “breaking-in process” would leave the plates looking used. Virtually all customers expect to see pristine plates when they receive them. Breaking-in a set of stones can be a relatively quick process if you know what you’re doing.
First, please understand that the plating process anchors a matrix of abrasive particles to the steel substrate. To make sure the entire surface is laden with abrasive, there is an abundance of particles applied, probably several particle thicknesses deep. The intent is that during the “break-in” process, you are knocking off all of the excess particles, until you have a substrate which is uniformly covered with a layer of diamond particles, each solidly anchored to the steel plate by the nickel plating. Those particles which were distributed above the base layer are much less solidly anchored and therefor are more easily knocked off.
By my experience, the lower the grit rating, the more difficult it may be to dislodge those excess particles. In some cases, clusters of particles may be arranged in such a way as to be difficult to knock off, especially if the cluster is arranged lengthwise. I can detect these clusters by feel and by ear. The stones make a very pronounced “click” as the cluster hits the edge being sharpened. Frequently, a new stone may show several of these “clicks” per stroke. You can feel it and you can hear it - it’s not difficult. When you have finally dislodged all of theses clusters, you are about 90% thru the break-in process.
For the last four or five sets of new stones that I purchased, I tried an accelerated break-in protocol (fancy name for “Ooh! Let’s try this!”). I clamped a section of 1/4" glass plate in the vise and slowly worked the stones over the edge. I instantly could identify clusters which needed to be knocked off, so I focused on those sections and repeatedly scrubbed the stone over the glass until the “click” disappeared. I used no more than normal force, unless a cluster was really stubborn. I doubt that it took more than twenty or thirty strokes on any one stone to clear it of “clicks.”
This wasn’t a sudden idea I had pounced on. I have done this in a number of cases over the last six or seven years, but not on new stones. My first case was a set of 800/1000’s which was giving me trouble. One of the 800’s was chipping the edge of my ZDP189 Delica. Badly.

I would have expected these stones to have been broken-in by now, but on inspection, I found a couple of clusters which were oriented lengthwise. This orientation made them more resistant to attempts to knock them off. Here’s one.

These clusters were really stubborn, so I tried the plate glass trick, and it worked. My new set of 2200/3000 grits stones were fixed from the outset and I was getting very good, if not excellent results by the second knife.
I would like to see WE supplying some version of my “break-in accelerator kit” and some good instructions on how to use it. It shouldn’t be a source of frustration to new users. For sure, there ought to be a video on the break-in process.
Oh, lest I forget, since the question was asked, a well broken-in stone will produce a smooth, uniform scratch pattern and there should be no tactile or audible feedback indicating that the abrasion is rough, bumpy or scratchy. You shouldn’t feel bumps or ticks that you can sense are produced at discrete points along the stone’s path. If you can tell that a click always happens at a certain point, mark the stone and check it with your 'scope or loupe. If you don’t have glass, work that particular section over the edge of a junk knife until it disappears. The click, not the knife.
If you read all the way to the end of this tome, thanks for taking the time, but you really oughta go have an ice cream cone or somethin’.