IT8 calibration is mainly intended for scanning positive film, using a slide target with known colors to characterize how your scanner reads color and build a profile from that.

For color negatives, calibration is much less straightforward. Negatives need inversion, and the orange mask has to be removed; that mask varies with the film emulsion, so a standard IT8-style calibration is generally not considered very helpful for negative scanning. In practice, most people rely on the scanner software’s negative profiles/tools and still expect to do some editing afterward.

For black-and-white negatives, color calibration is largely irrelevant. There’s no color balance or orange mask to deal with, so the main concern is getting a good scan with usable tonal range. You can then adjust levels and contrast in post. A specific calibration for something like 18% gray is usually not the key issue compared with making a clean scan and setting tones afterward.