I accidentally copied the text (a couple of hundred characters) of one cell to another, overwriting that cell, and discovered it too late to use CTRL+Z. I had a backup of that file on another HDD, and I found it using search. When I tried to open the backup, which contained he original contents of that cell, and tried to open it, to copy and paste its contents into the current version of the file, it opened only the current copy. I could not access the backup version! I had to rename the current file “…new.ods” in order to open it separately from the backup, and I could only open one at a time. So I had to close and save the current copy (renamed), open the backup, copy the text inside that cell, close the backup, open the current copy, and paste it into the bad cell. Then I had to close and save it again and rename it.
Also, even though the intention was a direct cell to cell copy and paste, which works within a file, it would not allow it, so I had to edit the cell being copied, select all (CTRL+A), copy that, close the cell and the file, open the newer file, edit the cell to be pasted, select all, paste, and close the cell. Why doesn’t the cell to cell copy work between files, as it does within a file (which apparently caused the problem to begin with) or between sheets in a file?