> What I have really is:
> <ptr type="bibliographic" target="heinemann"/>
> <biblScope type="number">Nr. 40</biblScope>.
> <author>H. Cornell</author>, Biblia pauperum,
Stockholm 1925, 81f. mit Taf. C,
> 46a und 48a.
In that case, I know I would feel tempted to have a <bibl> refer to
another <bibl> using the corresp attribute (which many consider to be
tag abuse, however).
Another temptation: redefine <listBibl> to allow <ref> (which won't
solve your other problems, so not really a temptation).
Correct but cumbersome: use <link> elements to establish links between
short and full descriptions.
But then the solution you propose seems quite reasonable too. I would
tend to use type="FullDesc" or something like that to make clear why the
<ptr> or <ref> is there (that the reference is bibliographic is clear
from the fact that it points to a bibliographical item, so there would
be no need to say type="bibliographic").