I try to maintain a coffee input of 17 grams (scaled). I am puzzled as to why 17 grams of coffee "x" often requires a different grinder setting than 17 grams of coffee "y". I use several different blends and keep a written record of grinder settings because of the considerable variation in grind settings.

I think you lose some of the fines grinding a darker roast. They get stuck everywhere.

It's a good question and probably nobody can tell you the whole story with certainty.

Coffees are different because they are agricultural products. There are different varieties, different growing conditions, and different processing methods.

Roasted coffees are also different because of the roasting level and profile. I think it's true in general that darker roasted coffees are less dense, more brittle, and more soluble. A less dense coffee, ground and tamped equally, will take up more space in the basket than a lighter roast. More brittle means more fines. More soluble means extraction happens faster, all else being equal. All three of these factors would lead one to grind more coarsely for a darker roast.

Storage conditions (both green and roasted), age, and grind temperature are additional factors.

It would be cool to read a detailed, comprehensive discussion on this subject.

Roast degree and bean density (affected by roast degree, crop conditions, growing altitude, varietal, etc.) are two main reasons. In earlier years of specialty coffee, David Schomer wrote chapters about adjusting the grind for an outdoor kiosk every 15 minutes due to ambient humidity changes. No clue if that stands up through time, but he was quite thorough.
Perhaps most importantly, changing the grind is essential to dialling a coffee in to the flavor _you_want_. It is a primary control for achieving your desired ratio.
If you run the same coffee consistently, you may find that adjustment is only infrequently required. But if you are expecting perfection, small tweaks may be needed regularly even as coffee ages, or with new batches of the same beans, and certainly with different coffees.
It comes with practice and tasting.

If you haven't, read these:
Espresso 101: How to Adjust Dose and Grind Setting by Taste
Mano Lite: A Short Guide to Dialing in Espresso SOs and Blends

Assuming you are using the same coffee for a while and not swapping daily, when dialing in, for more optimal results, try adjusting ±¼ or ½ gram [or golly, a whole gram ] along with a grinder adjustment to compensate. Additional basket styles will expand the possibilities.

The identical coffee from the same roaster, finca and year varies over time and requires adjustment in both dose and grind.

p.s. Please update your profile so we know what grinder you use. It can make a difference to advice.