Risk assessments are an iterative process that begin with an initial baseline assessment that uses the best knowledge available about the spacecraft and it’s mission. Additional assessments are performed as that initial knowledge is updated to account for changes in the spacecraft design and mission.
Also, some of the early assumptions and models as to how the spacecraft will respond to an impact must be verified by actually testing - shooting - parts of the spacecraft to simulate on-orbit impacts. Impact tests help verify some of the mathematical damage models assumed early in the risk assessment process. Many hundreds of shield configurations have already been tested and have damage equations available.
So, what do the risk assessments actually tell us? Well, they tell us which parts of the spacecraft are the most vulnerable to meteoroid and orbital debris impacts. They also tell us which size particles are a threat, how fast they move, and which direction they come from. Knowing this information helps us find ways to reduce the risk.
For example, if we see that a high-risk component would be hit by particles mostly from one direction, then a small shield could be placed in that direction to provide protection. Alternatively, maybe the spacecraft could be reoriented or the component moved to a less-exposed location. We also use the assessment results to verify the damage equations. The results are used to select projectiles (sizes, densities) and impact conditions (angles, velocities) for a verification test series in an efficient way so as not to waste time and money testing conditions that may not be relevant.