You can look at version history to see when (if) they were edited and restore a previous version

Thats the thing. I can't find any record of them in the version history and we've been using them for months.

The effects still exist, but the styles don't. There used to be four elevations which contained drop shadows which then used color variables which were tied to modes so that I could apply a single style for an elevation and it would be lighter or darker based on the mode.