I’ve wondered about this for a while...

Indeed - Roger Smith admitted doing this very thing when he was servicing watches in a presentation I saw a video of...

Well, he should have qualified that statement. While what your watchmaker says is true for many modern watches, and some vintage watches, for many older vintage watches this is not the case at all.

In some newer vintage watches and for modern watches, the portion of the regulating assembly that holds the regulating pins themselves is a separate part from the fine regulator or pointer. However for older vintage watches, this is all one piece, so if you move the regulating pins, it moves the pointer - they move together. So in the case of the watch above, your watchmaker's comments do not apply - the regulator is all one piece.

I think you are confused between being able to move the two parts separately, and there being some form of ratio of movement between the two parts. Here is a two piece regulator:



The regulating pins at the left arrow can be moved independently of the pointer at the right arrow. But when you move the pointer X amount, it moves the pin X amount as well - it doesn't have some sort of mechanism that allows the pointer to move X and the regulator to move some fraction of X, say 1/2 of X.

So just like on a one piece regulator, the amount you move the pointer is the amount you move the pins. The only difference is that they can be moved separately.

So to answer this initial question, when there is a one piece regulator as in the example you show, there is some work involved to center the regulator. On a modern watch as has been pointed out, you can move the pins and the pointer separately, but there that's not possible.

So how do you "fix" this? You have to add or remove mass from the balance. In this case the regulator is way over to the slow side, indicating that when centered it would run very fast. First, for it to be out this far is very unusual, so I suspect some kind of underlying issue is behind this state. The best thing would be to fix whatever that issue might be.

But say the watch has been gone over in detail, and you still end up with a regulator way off to one side. In this case it's an easy fix - add timing washers under the balance screws, and if the positional variation is good as it stands, you just add them in pairs opposite each other. Timing washers come in assortments like this:



The are designed for a specific size range of movements, and each vial contains washers of different thicknesses, that will change the timing a different amount. So on the far left are the thinnest washers, and adding a pair of those will slow the timing by 20 seconds per day. On the far right, the other extreme is a pair that would slow the watch by 4 minutes per day.

This is what the washers in the vial look like:



You have to be a little careful not to breathe on them when they are out of the vial, or they will be gone. These are very small, and to put it into perspective, here's a photo:



There is a 20 mm Omega spring bar there, and in front of it two larger screws on the right, and the small one one the left is from the balance of a watch - the screw I've added one of those washers too, but you can't really see the washer very well.

So why didn't whoever worked on this do these steps? Good question for them actually...

Wow, that washer is sooo small I can barely see it! Are these the smallest parts used in a watch movement? And how do you actually manipulate such a tiny thing?

Off the top of my head, I can't really think of anything smaller right now. Manipulating them can be a challenge. They are so light that they won't just dump out of the vial, because they cling to the sides. So you have to fish them out with tweezers, and I handle them with a very sharp pair of #5 tweezers.

A few things you don't ant to breathe in for when working on watches. This is one, but lume fragments are another concern certainly. Don't need any tritium or radium in the lungs thanks! 😀