As far as I am aware, the only ways that you would get an Album both under the correct Album name in the album View, and also in the unassigned group, would be;
1. You ripped the CD twice, and one version didn't get any metadata, so wasn't identified by Album.
2. You have Auto Import set up so that it is imported temporary files found in the MC cache. Although I'm not entirely sure that ripping a CD uses the Audio conversion cache. Something you could check.
3. You have Auto Import set up so that it sees the one location twice, and so imports using each path it sees. For example, if you had an F: drive in your server, which is where you stored music, in the directory F:\Music, and you also had a share setup pointing to the \\PC\Music, which is the same location. If both where set to be imported from, then MC would show two copies. If this happened though, both copies should be listed under the same Album name.
Also, make sure MC has had time to lookup the metadata and save it to the files, and refresh the Views you are using, before concluding that there are two copies.
If you find yourself in that situation again, with tracks visible both under the Album and unassigned, right-click on an example of each for the same track and select "Locate > On Disk (external)" and compare where the files are located. That may answer the question, and perhaps help you fix your Auto Import setup if that is the issue.
PS: As one of our experts here said recently, new pressings of old CDs can sometimes be very poor quality, as they are using old worn forms for the pressing. If you can't rip the CD you should take it back for replacement or refund. But maybe just a good clean would allow the rip to work.