I have been seeing a fair few answers posted by new users, where they are simply confirming previous answers. They usually run along the lines of following a high-quality answer with a one or two sentence version, that either re-states the same points, or follows the lines of "this is correct. I confirm this". That said, they still answer the question, in re-posting the same basic answer as the one posted, previously.
Looking on the Meta, I found this question and answer, which to me confirms that answers like this should be removed. However, given that there is no way to provide a custom reason when flagging, except for directly alerting moderators, the closest flag is "this is not an answer" or "low quality", and without comparing to the other answers, this reason can easily be interpreted as invalid.
In this question, we have an obvious candidate for answer attention; A question with a 50 point bounty. A previous user had answered the question, but OP is seeking "reputable sources". A user has since posted a poorly-put together sentence that only reiterates what the previous responder had said, and still provides no extra information or sources.
In this question, we have a user answering to confirm the previous answer, after already commenting on the answer previously, to say they had tried and confirmed the posters answer.
In this question, we have a user answering with almost the exact same information as the accepted answer. The only difference is they say that containers may stolen from. The say in the next sentence 'bandits don't come to steal, just invade'
In this question, we have the same user answering with two sentences, where the first is elaborated on in the accepted answer, and both are covered in a lot more detail in the other answer.
I found quite a few duplicate answers from the user behind the last two. They all popped up on review at the same time. Some of them were accepted, and the answers were removed. I noticed that I had flagged these answers as "low quality", while previously, I had used "not an answer".
That said, I noticed I had flagged the fourth dupe as low quality, and a moderator had directly removed the flag.
So my question is, when is an answer considered a duplicate? Under what situation should action be taken against a new answer that does not actually provide any new information? And if action is taken, what flag should be used?