From my experience, a lot of the CSM's and crew are just lazy and don't read the service manifest (if that's what it is called) properly. Granted, they are often just as confused as everyone else, but as I understand it, it is clear on each flight what service is provided, especially in regard to drinks. I'm often on the 18:30 SYD-CNS and for many months, flights departing between (I think it is) 18:00 and 19:30 are offered complimentary beer, wine and softdrinks in addition to the complimentary tea, coffee and water. Seeing I'm often in J, once the CSM has made their (incorrect) announcement from the top of their head, I often query it and suggest that beer, wine and softdrinks are complimentary. They scurry around for their paper, have a read and then sometimes update their announcement.
I'm sure there's lots of internal announcements that the crew have to keep up with, and I'm sure that many don't bother with keeping up to date and memorising what's what for each combination of route, aircraft type, flight time, length of flight etc. However, the information is available for them to access, and it annoys me that they just assume that they know what service to offer without checking. I know when I'm gonna have a good flight with a good CSM when they get the announcements right: fortunately, there are a few out there that are on the ball and they are probably the best CSMs within VA.