@Jay Hemdal This is an excellent topic to pick up again. I would like to add two things. As in all measurements, one thing is the mean value, and another critical value is the distribution of observations. The mean may be 76 days, but how wide is the range? I reckon it can be 30 days, ... or 100 days. Who knows.
The other thing is sensitivity of detection. The referenced work likely does not have the sensitivity that todays measurements would have, using for example quantitative PCR and high quality primers. So, at 76 days..., are there absolutely zero cysts left? There can always be that one lucky cyst that makes it back to the DT. So we should remember, we're reducing the probability, but can we be 100% sure? Likely not. And that comes back to the popular discussion: "ich eradication" or "management". I personally think ich is so pervasive that "management" is just the best word for it all. So in other words, if there is no equipment to detect every single cyst, how can you prove that eradication is the correct word?
My guess is that it would cost about 10K $ to get the critical data regarding ich stages updated. But that would only include disposables, and not equipment and labour. So, some valunteer scientist needs to take a 1-year sabbatical and do this.