Photoshop cs6 Frame Animation and Changing Opacity Over Multiple Frames

I have a frame animation containing layers that fade in by changing the opacity frame by frame.  The problem is, the layers were already in a number of frames prior to the fade in, at 100% opacity.  Not sure what I did but the layers that fade in have their opacity at 0% on all frames after the final fade in frame at 100%.

I assumed I could select multiple frames, select a layer and change the opacity to 100%.  I assumed this would affect the opacity for all selected frames.  It does not.  It only changes the first frame of those selected.  Conversely, if I select multiple frames by clicking a later frame and shift clicking an earlier frame, the opacity is only changed for the last frame (so it only changes for the first of many frames selected.  Is there a workaround?  I have hundreds of frames and a handful of layers and changing opacity by selecting each frame would be quite tedious.