Grant, I guess that the best possible suggestion is to go and read deeply Chap 12 of The RR Study Guide. The provision for In-advert Whistle are really thoroughly covered.
On the other hand I believe it would be interesting a discussion on how to avoid it in the first place.
Being oversea myself ... here in Italy we have the tendency to blow our whistle quite too often, several time also when we are not actually covering the ball (and this is done with some reasons - e.g. many rookies / inexperienced guys in crew, always changing crew and position and several others), but error remains.
Few Div I official we work with remind us:
1) play can end WITHOUT a whistle (e.g. incomplete pass / OOB runs)
2) the best is to have 1 whistle only (by the ball coverer)
3) no whistle shall be echoed (again ... in normal plays / normal conditions)
4) be slow with whistle - specially if in doubt
All this - of course - balanced by the fact that energetic whistling is necessary in case is needed to emphasize end of play (we - like in US I guess - coaches teach to "play to the whistle" ...)
PS I did not copy the RR to avoid copyright infringements ...
PS II sorry being so lenghty ...
