I can see why the base rules do what they do, and I don't begrudge it at all. I suppose I should have realized that having "starting 21 year old characters at 1610" is _sort_ of similar to having "36 year old characters starting at 1625", which the rulebook does have something to say about.
But yes, I agree that having expanded family history tables for other regions and time periods would seem to me to be useful and because they depend so heavily on Gloranthan lore not easily constructed for people who are only casually familiar with the background.