I occasionally encounter a case where an additional answer only adds information to an existing answer, instead of providing the whole answer by itself, e.g.:
Question: a question asking for a list of all nunchucks locations
Answer 1: a detailed list of 11 nunchucks locations
Answer 2: acknowledging answer 1 but mentioning two additional nunchuck locations not appearing in it
What do we think about answer 2? Technically it does not provide the whole list so it doesn't answer the question by itself - it depends on another answer - but it is still unquestionably useful.
Do we allow it as a separate answer?
- It seems to be accepted in the network
- It allows the answer to be voted on separately
- It gives credit - and reputation - to the correct user
- For many users, posting a new answer is easier than editing an existing one
Do we change it to be an edit for answer 1?
- It means a single answer will contain all the information required, a future reader won't have to browse through the entire list
- The important data will appear near the top of the page, we won't have anomalies such as answer 2 appearing before answer 1 because of it getting more upvotes for some reason
Do we change it to a comment on answer 1, mentioning that something is missing?
- This leaves control of answer 1 with its owner
- It may be less visible for future readers, though, if nobody updates answer 1 (for instance, because comments may be hidden)
I'm in favor of keeping it as a separate answer, but recently I've seen a few "not-an-answer" flags on these sorts of answers, so I wanted to make sure we have a consistent policy regarding these.
Also keep in mind the example I gave - adding to a list - is very black-and-white; other examples may include "answer 2"s in the form of "in addition to the strategy in answer 1, you should also supplement it by..." - i.e. another case where answer 2 depends on answer 1 and is not useful without it, but it's even clearer we'd want to have it voted-on separately.