Ben as far as letting grass get into the stemmy and seedhead stage as being better for "nutrients" I guess I don't follow that.

I am grazing mostly Dubuque red clay soils. These hold water but are not known for their fertility.  However the manure deposited from grazing whatever stage the grass is in is massive.

If you take an overall engineering view of a given pasture as a system, the only thing being removed from each grazing pass is the 3 lb per day ADG of the calves and maybe a slight addition to cow weight but not much.

Almost everything "harvested" by grazing comes out the back end of a calf or cow and back to the soil in a very useful available form. Even in my 10" to 4" system I see my soils and their productivity improving dramatically over the past few years, as you mention. Including improvements in the soils structure and its ability to support a load (tractor tires during mowing) with minimal compaction as long as the soil is not extremely wet when mowing.

And when I mow those seed heads and stems I am not removing them they are just being cut into small pieces by my flail mower and the hoof action of the nexty rotation works them back into the soil they came from.

Again I am not an expert at this by any means. 

My main, simple, laymans and engineers criteria for success or failure at grazing is looking at my cows: I never want to see any ribs (=BCS 5.5 - 6) if I start seeing ribs, regardless of what stage of lactation they are in, I am not doing my job.

Right now my calves are in the 90 day old range and probably near max load on the cows. Some are close to seeing ribs but not quite. I am starting to give them a bit more area on each rotation.

So in general, if your cows are maintaining condition, regardless of what grass height or stage they are grazing, you are probably managing right for your particular area. There is more than one way to skin a cat as they say. And rotational grazing in the Montana or Canadian ranges will be different than rotational grazing in Wisconsin which is different than rotational grazing in Missouri.

In my opinion, however, when I start seeing ribs on my cows I need to look into doing something different. If you look at the pictures of the cows in my picture in this thread (taken yesterday evening) you will not see many ribs. And they get no supplement other than mineral and maybe an average of one pound a week treat/training grain.

As usual, jmho.

Jim at Dawn