I am not advocating moving anything. To determine duplicates in a mail list, break it into its individual parts, score the matching parts, if your score is above the threshold assume a duplicate, save one of your original inputs (not the remix of parts).
You cannot know that "123D Main" is really the same as "123 Main, Apt D".
You cannot know based on that info only, but if I also have a matching zip, matching last name, matching first name, I may _choose_ to say that is a match, expecially if I am sending an expensive 4 color catalog at 80 cents postage per catalog. If I am sending a presorted one color postcard at the lowest rate (20 something cents I think), maybe I choose to say it is not a duplicate.