Overcorrection doesn't get you better vision any more so than putting on a pair of glasses much stronger than prescribed. If getting someone >20/20 vision was just a matter of dialing a higher number into a laser, every Dr. would do that. Correcting an eye to 0.00, or "plano", is the point at which a + lens or a - lens (ie: positive or negative addition of optical power) both cause a degradation of vision. This is why a manifest refraction involves an optometrist testing lenses iteratively until the optimal lens is found -- and the power of such lens is noted as your prescription.
But seeing that our prescriptions were similar, and we were treated on the same equipment, you probably were overcorrected, at least initially. If you're younger than me, you would've tolerated it with greater relative ease. The older you get, the harder it becomes to tolerate overcorrection. I spent a month being unable to read credit card numbers with ease during recovery. A 45-year-old might have spent 6 months in such a state. A 50-year-old probably would need reading glasses.
There's a lot of processes going on during the healing process. Cornea denuded of its epithelium produces a hyperopic shift in addition to whatever they remove to treat the myopia. The epithelium quickly regenerates, at least a thin layer does, reducing the overcorrection (edema makes it pretty much impossible to obtain a refraction, but its noteworthy that we were fitted with a +0.5 bandage contact lens for the initial recovery!). Eye dryness will have an impact on the optical power as well and will be myopic. The stroma itself "remodels", and suffers a myopic shift. And processes which are the root cause of myopia, such as axial lengthening, continue on post-surgical eyes and continue to cause regression themselves.