Actually, I think the regulations do address it, Chapter 3, Section 21:
Section 21. Call Backs. At the end of the first
series in each category (Junior, Senior and Master), and
every series thereafter, the Judges will call back all dogs
which they wish to evaluate further, and will score them
in additional hunting situations until the testing category
has been concluded.
Whenever a dog is graded “0” by two judges on the
same ability, or whenever it is evident that a dog can not
receive a Qualifying score, it shall not be called back to
run in subsequent series.