People would announce things like that to each group individually, and often chose to not mention it in some groups because they're not intimate enough. We used to just be okay hearing and discussing the same announcement multiple times ("some of you already know this, but..."), most likely with different parts of the story told in different settings and triggering different conversation because the groups are different.
For the more distant acquaintances, people wrote Christmas cards (or equivalent) for the occasional updates. These can still be handled very nicely with an email list, and really don't call for the kind of instant-update sharing that Facebook et al encourage.
Is it less efficient to write and read the same updates multiple times? Sure. But is efficiency really what we should be striving for in human relations?