Member. When you use the simple past "was added" it doesn't matter WHEN the action happened. If you say "has been added", as jinti said, it gives a sense of "recently", and also when you use it, the action has a consequence in the present, for example "an item has been aded (so now you can use it). Hope this helps!

Was added or have been added?

The perfect tense suggests a completed action in the past that is still relevant to the present. Thus, an item has been added implies that the item is still in the table of contents, whereas was added does not carry this suggestion, i.e., that item might well have been subsequently removed.

Were been or have been?

Let us say 'were' is a representative of the past tense, and 'have been' a representative of the present perfect tense.