Should a question about a particular haftarah be given the tag for the parasha that it goes along with? If so, what should be done about haftarot that are usually read with one parasha, but sometimes read with a different parasha? For example, the haftarah that is typically called the haftarah for Parashat Pinchas is very rarely read and instead the haftarah for Matot is read with Pinchas while the following week will be Matot-Masei and the haftarah for Masei is read.
Assuming that a tag isn't misleading, whether to include it on a question is a matter of priority, taking into account other tags that could apply and the limit of five tags total on a question.
Given that, I think that the following qualities should have more or less influence on prioritizing including a parsha tag on questions related to Navi text that's in that parsha's haftara:
If the question is about the connection of the text to that parsha, then the parsha tag should almost definitely be there, since the parsha itself is directly relevant to the question.
If the question refers to the text in the context of its being a haftara, then whatever parsha is referenced could be included as a tag, depending on what other tags are indicated. The fact that the question refers to the text in terms of its being a haftara is a good clue that other people might be interested in that text due to that context. Secondarily, any other parshiyot or holidays on which the same text is a haftara could be included, too, since the same clue applies, dilutedly, to the context of being in haftarot in general.
If the question makes no reference to the fact that the text is part of a haftara, but you think that some people might be interested in this text in the context of its being a haftara, then I'd suggest editing the question to include a nod to that context, and then, depending on other indicated tags, adding tags for whatever parshiyot's or holidays' haftarot the text appears in. Adding such tags without also editing the question could be confusing to people who don't realize that the text is part of a haftara.
I think questions about Haftarot should only be tagged with a Parsha if they ask about the connection of the Parsha to the reading. If it is just a local issue in the Navi, then its being a Haftara in some years/communities isn't relevant.
The Parsha-tag chosen should reflect the connection being asked about, whether or not it is the official "title" of the Haftara.
I think the question should be tagged with the name of the listed Parsha, even if it often is moved. The goal of tagging is to aid searching, so we should put a parsha-tag on, and this is the only system that doesn't involve guessing which is more common (is it more common for Haazinu to be Shuva or Shirat David?).