Ed,
Yes fuzzy dates are as much to deal with fuzzy human memory. There is no reason why we cant add things with more or less detail, as long as the way we interrogate the information is meaningful, other fuzzy aspects is you may not remember someones engagement date, but you may know it was before their marriage in the same year (or mealy before) for which you do have a date. Being able to record this fact before all details are available, and may never be available, is critical to tolerating missing information and allowing us to be fuzzy.
As I have said elsewhere being able to avoid loosing information, or encoding what information we have so far, is essential to extending the capabilities of ones wiki. For example if you remember the engagement was of importance, and you remember something about it, you want to record it and all you know about the date is "it was before the wedding" obvious I know, you should be able to capture the information, not represent it as a false date.
The fact is if you capture fuzzy information, it can facilitate the discovery of the real information, perhaps you remember it was just before your birthday, so now you can refine it more, and then looking in your diary just before your birthday you get the exact date.
I think the method is to find away to capture what you know in a frame work where you can interrogate it further. I would have milestone, events and periods, and an event has only one tiddler, and multiple levels of detail, eg: a year and month tag but no date, then when you find the real date you can remove the year and month tags because this information is in the date. Even your college years could be a single tiddler, with a date range, and this can become something you use for a fuzzy date. I Met him in college but don't recall when the date for the person tiddler is met in college date range, until something helps you realise it was in year two.
I imagine a hierarchy of decades and years within, and months within and days of month or days of weeks within them, and you get as precise, but only as precise as you can. The date hierarchy never changes so its stable, the more detail you have the path back to the root can be found.
I think the TOCP plugin is good for this.
Regards
Tony