MusiCAD tries to keep track of what you're doing, safeguarding your work by making backup copies in several ways.
Every time you start editing, the current file is stored in its entirety. If disaster strikes (like electricity blackout/brownout) you will be presented that copy.
As soon as you save your file, the previous version of your file will get another file-extension ( ~mc0, ~mc1 etc.) instead of the default .mc
Should you find out that a previous version was the better one, just open one of the backup files [File|Open]