Edit Hitsory

I jsut spent HOURS editing photos in colour and wanted to make the whole batch in black & White.I changed one picture to black and white , copied and pasted the edit settings to a batch of photos. How can i revert my pictures back to the last edit setting? USING COMMAND (MAC) + Z didn't revert all photos and stopped at about 10 photos. How can i revert my photos to the edit settings prior to B&W edits so that i don't lose my work and have to re-edit the all over again?