The Cambridge Grammar of the English Language (Page 1440) has this subsection
Adjectival passives with the negative prefix un
We have noted that such examples as the following are unambiguously adjectival because there are no corresponding verbs unrepair, unaccount, unsee:
 i The vehicle had to go unrepaired for several months.
ii Nearly half the money was unaccounted for.
iii He had remained unseen throughout the meeting.
[...] Secondly, the adjective may incorporate a preposition, as in [ii]. Although we have argued that in We accounted for more than half the money the sequence accounted for is not a verb, and not a syntactic constituent, the unaccounted for of [ii] is a compound adjective. The difference in status is reflected in the fact that the verb can be separated from the preposition whereas in the adjectival construction the parts are inseparable. Compare We have accounted already for the money and *The money was unaccounted still for.
Thirdly, the morphological process of forming such negative adjectives is highly productive, and in many cases the form without the prefix occurs in verbal but not adjectival passives. For example, unseen is an adjective, but seen is not: compare [43iii] with *He had remained seen throughout the meeting.
With this in mind, let's take a look at the following passage from a 2013 New York Times article:
One reason many 19th-century ballets are called classics is in their mastery of patterns. The geometries we see in “Giselle,” “La Bayadère,” “Swan Lake” and “The Sleeping Beauty” remain the archetypes for opera-house-scale legibility. But here, Balanchine, drawing from their precedent, remains the master.
More than anyone else, he knew how to make movement animate all of the box of space behind the proscenium arch. Every cubic inch of air seems accounted for — most powerfully if you saw his ballets danced by his own company in his lifetime.
According to CGEL's analysis, the accounted for of the last sentence seems to be a compound adjective. And in CGEL's [43 ii], the unaccounted is an adjective.
The question is whether the accounted in the NYT article is a verb or an adjective. If it's a verb, the verb phrase accounted for somehow functions as a compound adjective. If it's an adjective, accounted for is not a verb phrase but an adjective phrase. Which is it?
I have what I think is an important question about CGEL's claim:
[T]he verb can be separated from the preposition whereas in the adjectival construction the parts are inseparable.
To support the claim, CGEL shows this example:
(1) We have accounted already for the money.
Here, the verb accounted can be separated from the preposition for.
Now, the passive construction of (1) is:
(1') The money has been accounted already for by us.
Here, accounted is still a verb, but can it be also separated from the preposition for? Does (1') work? It doesn't work for me.