It would be hard to tell you from the information that has been given. Lightroom edits are stored in the catalog. Unless you had all of the images highlighted, auto-sync enabled and clicked on the Reset button, theoretically your editing work should still be intact. You might want to revert to your most recent backup and see if that resolves your problem. Otherwise, we would need a lot more information about what REALLY took place.
In addition to what Jim said, another possibility is that when the import was done, you (accidentally) copied the photos to a directory that you really didn't want them to go to, and then edited the photos. So looking in the date folders won't find them. Some people then import the photos a 2nd time, giving them an unedited copy and an edited copy.
If you go to All Photographs, and search for the photos by file name (click on Text, set the dropdown to File Name and then type in the file name of one of these photos), do two copies appear, one edited and one unedited?
Exactly! It's very hard for me to give you information unfortunately
because I have no idea what happened. I'm just going to go back and re edit
and hope this doesn't happen again. Thanks for trying!