Root length is proportional to grass blade length and certain grasses can die from scalping. It could be your grass is coming back slowly. That is the nature of many zoysia varieties. Zoysia also recovers very slowly from fungal diseases. It could be you had some of that going on, too. Or you may still have some of that going on. I would reset the mower deck height to 4 inches if you have that setting available and let the grass that is still living do its job.

My idea of scalping is as low as any given mower will go while still able to move across the turf. This depends on the smoothness of the turf, the type of turf, how thick it is, whether it is dead or not, etc. When I scalped my toasted RUed KBG yard, the only thing keeping the mower from moving was the level of the lawn, so I was on the second to lowest setting. This left close to nothing on top of the thatch layer. When I came to the areas that I had missed with Roundup the first time and were still green/living/thick, I had a real problem at this level. Mower bogged down big time. All depends on the conditions of the turf and what the mower is trying to roll over and trying to knock down. The long germination time of the new KBG was the reason I went ahead and killed the existing lawn. I didn't want to go to all this effort just to have the old KBG fight off the new elite seed.

One other thing I've always thought, "stunning" existing grass a bit when doing a heavy overseed actually might not be too bad of a thing. The new seedlings can get a better start without a lot of competition (getting shaded out, etc.) from existing grass growing right back up. You can actually buy growth regulators to slow the existing grass down for awhile to help the new stuff out. I've never done that, but, cutting it low, giving it a pretty good beating with an aerator, etc, has always seemed like a pretty good thing to me. Plus, my experience has always been that about six weeks out, after all the extra water and fertilizer, the old grass will look great, especially with the new helping fill in.

Dchall was responding to your question about the lawn now being more susceptible to weeds. He was kidding you to say if you want weeds, then water every day. He was not suggesting you do it, and he would not suggest doing it under any circumstances. What your refer to as being more susceptible to weeds is simply that the lawn is now cut to such a short length that it no longer shades the soil, thereby exposing weeds/weed seeds to air and sunlight. Every plant needs those, but taller grass helps to prevent weeds by depriving them. I was suggesting that because it could be in shock from mowing so much off at once, it could be more susceptible to disease it may have been vulnerable to in the first place. In its shocked condition, it is in a somewhat weakened state and not able to keep fighting off something it is already open to. So, just keep an eye on it. I think we're all trying to say you really don't have to worry or do anything in particular right now except water it, which I'm sure you've done by now. I know you are concerned but don't have to be, and basically you cannot help it recover. It will do that quite on its own. If I were to suggest adding anything right now, it would be corn meal for its anti-fungal properties to help fight disease. But then, I would suggest that anyway. I'm kinda wondering if you know what we mean by "water deeply" or "water 1 inch" or "water infrequently." Please understand no one wants you to water your grass every day. That absolutely cannot help it to recover from being mowed too low. It can only cause very awful problems. We want you to water it just 1 inch all at once, and then not again until the next week. Deerslayer is explaining you must take rainfall into consideration. Your grass needs 1 inch of water each week. With 3 or 4 tuna cans placed in various places for your sprinkler to reach evenly, time how long it takes for the cans to get just 1 inch of water in them. That is how long it will take to provide 1 inch of water to your lawn. It might be 45 minutes. It might take an hour or more. It just depends on your sprinkler system, but you want to water for that amount of time. You want your whole lawn to receive 1 inch of water, so if there are areas that do not get any water, then position the sprinkler to irrigate 1 inch in one area, and then move the sprinkler to irrigate 1 inch in the other area. Hope I explained things a little better.