Flare would tend to limit the low end of the characteristic curve, with relatively little effect on the dynamic range. Most of the dynamic range of B&W film is in the upper reaches of density. That said, it is the abscissa, exposure, not the ordinate, density, which is a measure of dynamic range. Published curves for Tri-X start near zero and stop at a density of about 3.0, at an exposure range of 3.5 log(lux-s), the latter corresponding to a dynamic capture range of 12 stops. At that point, the response is almost linear, which means the shoulder of the curve is unknown. When completely fogged, Tri-X reaches a density of at least 5.0, which represents 17 stops off the film. In order to have a capture range of 18 stops, you would need an exposure range of 6 log(lux-s), which is not unreasonable, if not actually practical. Processing which reduces the slope (gamma) is practical, however, and would have a profound effect on dynamic range.