For events 400 m and less, three times the racing distance is enough. Too much anaerobic work will precipitate overreaching and if continued, overtraining. For events more than 400 m, two to two and a half times racing distance is enough. Remember, the interval sets included in these interval-set distances are at intended race pace, not slower nor faster. Speed up the race pace equivalent, reduce the distance, and start building up to the maximum distance again.
Work done beyond adaptive work is counter-productive and negates the benefits of useful training.
This is the tough part of training for individuals who have strong work ethic. When you are not doing race specific work, the remainder of swimming should be building or maintaining aerobic base or recovery. That no longer is true so the concept is no longer relevant. There just is no place in beneficial work for damaging fatigue states to be endured. I rely heavily on German research to support this contention with backup from David Costill's laboratory at Ball State University.