Blender files not recognized.

I am new to blender, and I am using a Mac. I have several iterations of one blender project. Iterations 1-10 will open but 11-28 will not open. Even though they are saved as .blend, blender is saying that they are an unrecognized file format. The reason why I have so many iterations is because I was unwrapping one object at a time and saving each time before doing to much and making a mistake that I could not undo. Is there a way to get these files to open? I also exported them as .3ds and .fbx. If anyone has any suggestions on how to reopen these files or more efficient workflow practices any input would be greatly appreciated. Thank you.

Try appending (Shift+F1) the objects from the problem blends into a new blend. It way be one particular object that is a problem so try appending one object at a time.

also report i as a bug
might help to correct this problem!

salutations

Set it as your default so when you make a new file it shows up instead of the cube