for now the best way is to check past notices.
our subscribe-o-matic, (SOM) is used in the same way the "quiet" group is used. for major releases, etc. the SOM due to the way it works is not a viable option to send out things like traits, etc... one message can take 4 to 6 hours. (it is determined by group size) so that would not solve the problem of getting news out fast to a large group.
we send a lot of notes in the "addicts" group that keep with the tone of the chatter, fun, etc. the best way if one wants to get EVERY one of those is really to check the notices as yes, SL can be very unreliable. it's not just large groups, some smaller groups i am in i miss the notices too! the interesting thing is, some i don't really care that much about i seem to get notices all day long!!! go figure!
so for the most relevant news, we will always post that in both groups and the SOM, and the forum. for the extra fun stuff, that can often be many on some days... especially when the cats post
we will use the Addicts group and everyone can check in past notices as they are kept for 2 weeks!
hope that clarifies a bit!