Coop,

<...makes a difference between a good negative and a really good negative...>

FWIW, here's how I think about it; it's in relation to the characteristic curve of the negative; the paradigm being an S-shaped curve. [I said paradigm; it's a general discussion; I recognize some film curves have a different shape.]

The low values are captured closer to, or at, the "toe" of the curve (where it's not very curvy) and the high values will end up at the "shoulder" of the curve (another place where it's not very curvy). In between is a relatively straight line.

Values that end up on the toe (low values) or shoulder (high values) will be compressed, with less separation between them, compared to values that end up on the straight portion of the curve. Values that do not have good separation have less information.

Exposure mostly affects the low values. Exposure will set where low values end up on the curve (usually the toe ranging into the straight line portion). For high values, exposure and development together control where they fall on the curve (usually from the straight line ranging into the shoulder). [Development will have some effect on the low values, but that factor is usually ignored.]

For any given combination of 1) subject brightness range, 2) exposure, 3) development, you can see that a photographer can shift that range up and down along the film curve.

When someone talks about exposing important low values for Zone III or Zone IV, what they are saying (and all that they are saying) is, for that part of the subject, they want to be sure they record enough information, far enough up along the curve (away from the poorly separated toe area) to be sure that information will show in the print [and, in the ideal situation, with latitude to allow for alteration through printing procedures]. But, of course, the higher you place the low values, the greater the risk you will move your important high values too far up on the shoulder (because of the inherent subject brightness range between high and low combined with the amount of development you give the negative). Values that end up too high on the shoulder become "blocked" and will only print as extremely light grey or pure white, without detail of any kind. (Again, information loss.)

A "good" negative in this sense doesn't mean that you are necessarily dealing with great subject matter. It only means that, because of your choices as to 1, 2 and 3 above, the negative contains enough information in the low and high values that were of importance to you when you exposed and developed the negative, that, in making the final photograph, you will be able to print the negative as you wish on photographic paper (or a computer monitor, if that is your goal for output).

In that limited sense, a "good" negative becomes (in theory!) easier to print the more the important subject ranges (low and high) end up on the straight line portion of the film's curve. On that portion of the negative, you know you will have good (ie, printable) detail and good separation of tones. And then it's up to the printing of the negative to keep or to change those values, depending on your artistic intention for the final print.

This stuff is far more cumbersome to write about than it is to understand.