future perfect continuous negative

Another extremely rare but listed grammar structure is future perfect continuous negative.  On iWeb there are only a few occurrences:

1 WO N’T HAVE BEEN LIVING 5
2 WO N’T HAVE BEEN DRIVING 3
3 WO N’T HAVE BEEN EXPECTING 3

iWeb won’t even allow a search for “will not” saying there are no entries!

It would seem that “English Grammar Profile” adds entries like this (point 42 in their future category) as symbolic place holders.  They are confusing though because they seem to undermine the point that they make that all their grammar points are given levels based on empirical evidence in their corpora.  If there are no examples of such a point why give it a level?  It makes you wonder whether all their rarer points are given a level even though there may be only a few examples of such.