The mirror should be easier to see the damage. You can look at the surface. You should only see a perfect reflection. Damaged mirrors may see pitting, black or brown stains, cracks, scratches, burnt material deposits, etc. Even brown haze can be a sign of damage.
I have a professional client who claims that his mirror is perfect. We only changed the rearview mirror for testing and found that the power increased by about 15% to 20%.
The lens is more difficult to check. The translucent orange lens is obviously easier to check than the dark purple black lens. Likewise, you should look for scratches, cracks, pits, material deposits, smog, smudges, etc. The difficult part is to see if there is any smog caused by overheating inside the lens. We can’t see the same range of light as a laser…so this is our best guess about how good a laser lens is.
I recommend that you clean each mirror and lens gently (thoroughly). Use alcohol first, then acetone. Switch back and forth until all blemishes disappear. The idea is not to scrub or wipe with any pressure. You should only use lens cleaning paper or Q-Tip (use a cotton swab with paper or a wooden stick. Acetone will dissolve the plastic stick or nylon cotton swab.) Apply alcohol to the lens. Let it drip or evaporate. Your final cleaner should be acetone, because it can remove stains from alcohol or watermarks.