[Christ]

It's OK to re-cover the same information, because there are always newbies and new information might come out. People who complain that "it's already been covered X-long ago" aren't usually interested in actually advancing technology so much as just talking about it, so don't worry if you bring up something that's already been covered awhile ago, especially if you don't understand. Better to explain something 20 times to people than have 20 people mis-explain it to someone else.