Question: My relative, with debilitated Mercury, has communication problems and suffered an injury to his nerves. Over time the communication problem has improved, but the injury has not. Why?
Answer: Your question seems to be, “Why has one thing related to Mercury improved, while another thing related to Mercury has not? Shouldn’t everything related to Mercury improve if Mercury improves?”
Take the colors of the spectrum. Theoretically all the infinite colors are made by only three: red, yellow and blue – plus lightness and darkness. But in nature you never find any of these three primordial colors in a pure state. They are almost always mixed and blended with one another to create all the rich varieties of colors we see all around us.
Astrology is the same way. There are 8 or 9 planets, and those few make up the INFINITE outcomes of all the different human beings throughout history; much in the same way that three colors make up all the infinite colors in the universe. Just as you almost never see a truly pure blue, yellow, or red in nature – similarly you almost never see anything in life is entirely the result of a single planet.
Everything is a result of several planets combining. For example, speech is mainly a topic of Mercury, but Jupiter and Venus are also quite instrumental in giving us good oratory skills. The nervous system, as another example, is mainly the topic of Mercury – but an injury to the nervous system will involve a malefic planet, especially Mars. Dance, music and other expressive arts are Mercury skills, but they require lots of cooperation from Venus. Recreation is Mercury, but how can you be playful without the right frame of mind (Moon)? Astrologically, nothing is a result of only a single planet, everything is a result of planets combining in various ways.
So, Why does one subject of Mercury improve over time, while another thing connected with Mercury does not? The answer is that the subject which improved involved Mercury with another planet(s) who is positive in the horoscope and was influential in a timely manner; while the subject which did not improve involved Mercury with another planet (s) who is negative in the horoscope and/or did not yet have a chance to have a significant chronological influence.