It was not my intent to make any "blanket statements." Notice that I said merely that a mirrored surface would reduce the missile's vulnerability - perhaps even enough to allow it to survive, e.g., a "near miss."
It has been demonstrated in lab tests that the energy transfer is enough to destroy a target.
As long as those lab tests included such real-world factors as the atmosphere's intrinsic opacity, possible interposing clouds, the gradual widening of the collimated beam, etc., I will accept that.
You should probably also factor in any contamination of the mirrored surface such as dust, dirt, oils and anything else that could absorb the energy.
What happens is that no reflective is perfectly reflective. Absorption of even a small amount of the laser's energy damages its reflectivity, which causes it to absorb more energy, etc.