They do have a rather strange numbering scheme. There are 12 "issues"
per year, and the volume number is the same as the year number, and
really is 4 digits. (Most online-only journals (unless, perhaps, they
have a history of paper publication) tend to have one volume per year,
usually starting at vol. 1 whenever the journal was founded, and article
identifiers instead of page numbers, with no issues or numbers within
the volumes. Example: https://astro.theoj.org/ .)

ADS tends to treat their issues like volumes in their identifiers (which
normally don't have issues or numbers), but this isn't completely
consistent since they start over at 1 every year whereas volumes are
usually continuously numbered. Of course, together with the year it is
a unique identifier.

Actually, they aren't even consistent themselves, recommending citations
such as JCAP08(2016)013 which, aside from being ugly, would normally
suggest vol. 8, p. 13 from year 2016. Bu their website clearly
indicates that the volume number is the same is the year and that the
other number is the issue number (usually, in most journals, not given
in the reference list).

So for, say, volume 2013, issue 5, id or page 37 there would be the
choice of

5, 37, 2013

or

2013, 13, 2013.

if the order is volume, page, year.

There doesn't seem to be an official recommendation, and like I wrote
the journal itself is inconsistent.

What do people here do? Is there any official recommendation?

Of course, with links to the DOI in the reference list, the actual form
is less important than it once was. Still, many journals, whether
electronic or paper or both, still have conventional reference lists.