It’s been a rocky ride over the last 12 months for many of L.A.’s publicly traded companies. All told, 63 of the 100 firms on the Business Journal’s list of public companies this year posted net drops in their market capitalization – or total value of their stock – for the year ending June 30. And the damage was pervasive, touching just about every industry, including real estate, manufacturing, biotech, health care, entertainment and retail. (The List of Largest Public Companies begins on page 16.)