The S.I.s would have needed to take exception Appendix A "A2" and specify some other scoring method in order to NOT have any throwouts. You're thinking of the SI's that specify a throw-out after four races - they're making an amendment to Appendix A to keep from having a throwout after two races.
89.3 Scoring;
The race committee shall score a race or series as provided in
Appendix A using the Low Point System, unless the sailing
instructions specify the Bonus Point System or some other
system. A race shall be scored if it is not abandoned and if one
boat sails the course in compliance with rule 28.1 and finishes
within the time limit, if any, even if she retires after finishing or
is disqualified.
.
.
.
From Appendix A:
A2 SERIES SCORES
Each boat’s series score shall be the total of her race scores excluding
her worst score. (The sailing instructions may make a different
arrangement by providing, for example, that no score will be excluded,
that two or more scores will be excluded, or that a specified number of
scores will be excluded if a specified number of races are completed.
A race is completed if scored; see rule 89.3(a).) If a boat has two or
more equal worst scores, the score(s) for the race(s) sailed earliest in
the series shall be excluded. The boat with the lowest series score wins
and others shall be ranked accordingly.
