Nephelornithidae Wolters and Poospizinae Wolters must have the same status.
If you apply the Code down to the word, "every new name" published after 1930 requires a description, unless it is a "new replacement name". Neither Nephelornithidae nor Poospizinae is described by Wolters and they are certainly not "new replacement names", hence they are both
nomina nuda in this work. If so, if they are to be used, another source must be found that would satisfy all the requirements of the Code.
Bock 1994 did not see it this way, however. Bock wrote (p.98):
This requirement [Art. 13] of the Code is absolutely essential for species-group names and presumably also for generic-group names, and its inclusion in the Code was definitely intended for these names. Its application to family-group names is excessive, because the proposal of a new family-level taxon and its associated name is totally unambiguous if that name is firmly affixed to a type genus. Moreover, this requirement for availability as stated in the new Code (ICZN, 1961) was applied retroactively to family-group names proposed between 1930 and 1960; the provision in the Règles [Art. 25(c)] applied specifically to generic and specific names. Almost all new avian family-level names published after 1930 were not accompanied by the required description of the characteristics of the new taxon. This includes almost all names published after 1930 which are currently widely accepted and used by avian taxonomists. Most likely the same situation exists for other groups of animals. Because it is clear to which taxon a new family-group name applies if the type genus is given or is clearly implied, avian family-group names proposed after 1930 will be accepted even if they do not comply with the requirements of Article 13. To do otherwise would cause great chaos and the need to propose anew most of these recent names. An application will be made to the ICZN to modify Article 13 to exclude family-group names from its provisions.
Under Bock's rules, Nephelornithidae Wolters and Poospizinae Wolters are both available, because they are based on a type genus that is clearly identifiable. (If so, if it has the same date of publication, Nephelornithidae has automatic precedence over Poospizinae.)
However, a new edition of the Code was produced since the publication of Bock's work, and Art. 13.1 still says "every new name", without excluding the family group... And a significant proportion of the family-group names proposed over that last 20 years have indeed been names that had been proposed before, for taxa that were not described, and were being proposed anew ("formally"). IOW, at least a part of the taxonomists have apparently accepted Bock's "great chaos" and are dealing with it.
(OTOH, note that even those who insist on the requirement usually exempt family-group names that were explicitly proposed to "replace" another family-group name due to the synonymization of its type genus. This is arguably completely illogical. The nominal type genus of these names is
never, by definition, the same as that of the name they "replaced". [Or should it be "displaced"?] The Code defines a "new replacement name" as having the same type as the name it replaced: these names
cannot be "new replacement names". [If one insists that they are, they
must be based on the nominal type genus of the name they replaced, which was treated as invalid in the publication that introduced them; as a consequence, these names fail to satisfy Art. 11.7.1.1 and are --
all -- unavailable...] I see no support in the Code to exempt these names from the requirement of a description any more than any other.)