I think it is very much definitional. It's a matter of deciding what is mandatory, and then mandatory is mandatory. If a department says that something is mandatory, that's going to attract auditors. We take their word that it's something that has to be in place.
If there is an area in which something doesn't need to be mandatory, then just say it isn't mandatory; don't make it mandatory in that part of the organization.
Probably in this case, if we accept that there's always going to be turnover and ask how we get to 100%, the question can be better dealt with by a clear definition. For instance, a definition could require that within so many days of being hired, it is mandatory for a person in a given position to take a certain type of course.
The problem we have right now and when we do the audit is that when we see that something is mandatory, we go in at a point in time. If somebody has just been hired the day before, it's probably not reasonable to expect that they will have followed their values and ethics training by that day. When we do the audit, we pick a point in time, and there is no definition, really, of what “mandatory” means.
I think that if there is a clear message that a given type of training is mandatory for people in given positions and that mandatory means mandatory within a certain time frame—you have to follow the training in x number of days—then you have something for which the expectation is clear, reasonable, and measurable.