op. cit.

OK, I really, really hate having to do this, but I think we need to
add support for op.cite/supra references. From the Zotero forums,
explaantion fo how it works in Bluebook:

“I think that the biggest additional problem raised by bluebook over
other styles is that after the first cite, subsequent cites have to
refer to the footnote number of the first cite. So if an article X is
first referred to in note 3, the subsequent short form is” X, supra
note 3." This in turn means that every time the piece is edited and
the footnote number of the initial reference changes, every subsequent
supra cite has to change also."

The tricky part is figuring how to specify “note number for first
occurrence.” If we’re lucky, the solution is already in CSL in the way
that “number” style citations work, but I’ll need to check.