Well if there had been enough improvements to the emulation to warrant removing the NOT WORKING flag, then it would have been listed under the 'new working machines' section.
The flag indicates zero confidence is the driver running properly and is used for machines that don't do anything, are liable to crash at random, or have serious game breaking glitches due to incomplete emulation. For non-arcade drivers they can also indicate a low compatibility rate for the software that is available for a given system (ie, again, a flag of no confidence in the correctness of the emulation)
If there had been noteworthy progress on the driver more people would be making a big deal out of it and the flag would be gone ;-)