I downloaded version 3.3.7491 from the MB website. Regarding opening by holding the shift down, what do you mean? I tried holding shift down while double-clicking on the desktop icon, while right-clicking on the desktop icon and selecting open, and selecting open as administrator. In all cases, when I then go to file -> Library -> Open Library, I get the same library every time. However, when I navigate to the .mbl file itself, right click on it and select Open, I DO get the select library question. HOWEVER, is there any chance of my messing up what I have by doing this? I'm never clear what happens automatically when opening MB.
The major problem I still have is that there are many duplicates. One thing I did yesterday was to add Filename and Path to the displayed fields to identify where the audio files were located and, where there are duplicates, often the two files are in different directories. If I delete the one which is in the "wrong" directory, is there any chance of messing up the tags? Again, where are the tags stored - in the audio file or in some database?