tense-aspect --> ZAhO?

[Ivan A Derzhanski <cbmvax!uunet!cuvmb.cc.columbia.edu!iad>]

Re things like {le mo'u zdani}...

My knowledge of Lojban grammar comes chiefly from the BNF version
(24.2.1991), and it lists the following basic types of tense-aspect
tags which can be used alone or in combination:

BAI  (modality);
ZI  (scalar magnitude of tense);
PU  (tense, time-offset);
<number> roi  (quantified tense);
TAhE  (tense interval property);
VA  (distance in space-time);
FAhA  (superdirection in space-time);
fe'e <interval-modifier>  (space interval distributive aspect);
CAhA  (actuality/potentiality);
fi'o <selbri>;
cu'e  (interrogative).

It doesn't say that ZAhO can be used independently as a tag without
being preceded (and eventually followed) by an <interval-property>.
What is going on?  Is the BNF grammar just incomplete in this regard,
or has this usage become legal after 24.2.1991?

Ivan