I just noticed a second bracketed prepending [PROPOSAL] and realised that I was on about were nouns and the bracketed stuff are adjectives, or possibly verbs.
[ANN] and [PROPOSAL] seem like adjectives to me because they are describing the kind of posting, but not what class of thing the announcement or proposal is about.
So, that would tend to make NEWLIB redundant because it is not simply a noun because it describes state. However, it might be useful anyway to use both NEWLIB:[ANN] and LIB:[ANN]. I'm not sure, so I'll let that one through to the keeper for now.