In this area, the dates are totally wild guesses. There is no documentation - and I do mean *no* documentation. All we have is a couple of sagas that have ancestry lists. Merges have carried various people's "one generation back, the date has to be this" numbers together, and not consistently.
A number of them seem consistent, though, so it's possible that there's a source somewhere out there (probably 19th century - they were good at stating wild guesses categorically as facts) that we could quote - but the alternative is just to produce another random set of numbers and slap them in there, which is something I'm loath to spend time on.
Dates can be kind-of-useful as long as we remember not to believe them. At times (especially the Frodes in the Danish lines), the dates make it somewhat easier to not do broken merges.
Besides, if we delete the date, all it means is that it gets filled in at the next merge, because we've got no way of marking a field as "intentionally empty".
I disagree. Even if you have to average out ages between two know dates when you come to a difficult line if you can't come into realistic norms by averaging the line is no line at all. I cannot keep unrealistic and un-averagable line in my database, dates or no dates. For Bible people I substitute scripture location in place of dates.