Also, the status field is mentioned in the official list of fields, with "forthcoming" as an example value, so presumably something like this is actually used in other formats.

Ah, I see that this is implemented in the zotero APA CSL file: http://editor.citationstyles.org/styleInfo/?styleId=http%3A%2F%2Fwww.zotero.org%2Fstyles%2Fapa

Is there any reason why it's not implemented here?

To support these, the apa.csl file would need to check the status field and change the way the issued date and the journal, volume etc.

We can probably improve support in CSL a little bit (e.g. with a controlled vocabulary for the "status" variable), but of the three statuses you list, "In preparation", "Submitted", and "Advance online publication", you would typically only cite items with the last status in your bibliographies. Currently, we assume that authors just write out references to "In preparation" and "Submitted" items by hand in the text.

To determine if an article is "Advance online publication", CSL styles often check if the item is missing an issue or page numbers. (@adam3smith, correct me if I'm wrong here)

Ah, I see that this is implemented in the zotero APA CSL file: http://editor.citationstyles.org/styleInfo/?styleId=http%3A%2F%2Fwww.zotero.org%2Fstyles%2Fapa

Is there any reason why it's not implemented here?

That's the style from this repository (I recognized that it's a bit confusing that all CSL repository styles have style IDs with the Zotero domain in them, but that's just how things developed historically).

@rmzelle No, in psychology and management journals, it’s common to cite in preparation and submitted manuscripts. But those get cited as manuscript not article-journal. From APA perspective, there are two statuses that should be supported: “in press” and “Advance online publication”. It would be good for these two to be implanted as terms (e.g., NLM and Chicago recommend “forthcoming” instead of in press).

@kleinschmidt The first two examples at the blog post you link to would be entered as Manuscript with the “status” in the Manuscript Type field. CSL type manuscript and CSL variable genre

@rmzelle @adam3smith I've been thinking about how to improve the use of the status variable and related terms (forthcoming, in press, etc.) in various styles. I think that most use cases can be covered with a controlled vocabulary with three options:

1. forthcoming: Indicating that an item is accepted for publication and somewhere in the production process. This status would call the terms in press or forthcoming as specified by the style.
2. advance-online-publication: Indicating that the item has been published online but not yet assigned a final volume/issue/page ("ahead of print"). This status would call a new term advance online publication.
3. User-supplied text, to be printed literally.

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@bwiernik If in preparation and submitted manuscripts are actually cited in some journals, shouldn’t these terms be included in the controlled vocabulary?

Those sorts of things are typically stored in the genre CSL variable with manuscript item types.

advance-online-publication: Indicating that the item has been published online but not yet assigned a final volume/issue/page ("ahead of print"). This status would call a new term advance online publication.

I'm not a big fan of this because it implies that publications aren't online, and/or that online publications aren't real. In science, at least, referencing dead trees is becoming less and less meaningful. I appreciate that most citation machinery has a lot of history behind it, but there's no reason to intentionally put ourselves in a box where we pretend the internet isn't fundamental to the way that people access citeable works. advance-publication is fine; there's no reason to specify "online".

CSL tries to be mostly policy agnostic (there is no rational justification for the existence of most citation styles in the first place, after all...). The publishing system uses a lot of old-fashioned terminology (cf. also "preprint"), but I don't think the place to change that is in the syntax of a programming language. "Advance online publication" is very widely used, so using that as the attribute just seems like good literate programming practice to me.