If I understand you correctly, simply (in Lightroom) click on the top level folder (right hand panel in Library panel). You should see all images. If not, Library menu -> check "show photos in subfolders" (but if you're looking for stuff in the top level only, maybe you want to uncheck this option). Then use the Library Filter towards the top, click Metadata to show date options, and you should be able to choose the date range affected. Select the images you want to move, and drag them to the right folder. If the folder doesn't exist, you may need to create if first (in Lightroom - right-click the parent folder and "Create folder inside..."). Clearly if there are lots dates to go into lots of new folders, you will need to do this a few times, but even for "many hundreds", and even if you want them in lots of different dated folders, it shouldn't take more than an hour or so.
That all sounds pretty simple to me, so maybe I've misunderstood your problem. I also keep stuff in dated folders and subfolders, and like you occasionally import into the wrong folder, and have to drag stuff around to the right place.
This did it! Thank you so much, it didn't take much time. The key points were unchecking the "Show photos in subfolders" so that only the misplaced photos in the root folder showed, and then using the Filter option to sort these misplaced photos by date. I was able to quickly move them into their respective dated YYYY-MM-DD subfolders. Thank you!