The Belisarius series-
1. An Oblique Approach
2. In The Heart of Darkness
3. Destiny's Shield
4. Fortune's Stroke
5. The Tide of Victory
6. The Dance of Time
Thunder at Dawn looks to be a reprint omnibus. Baen does quite a few of those. The ebook versions of the omnibus editions are usually a very good deal by the way.
There is also a novella in
The Warmasters collection. I'm not sure where it fits in the continuity of the series.
Matter of fact, it's the only new thing in the collection.
The other two pieces are reprints of David Drake and David Weber pieces. The only real complaints I have about Baen are that it is sometimes hard to know whether or not something is completely new. For example, The David Weber book
Bolo! only has one new piece (which is actually a prequel to his novel
Old Soldiers) but you can't really tell that
With Your Shield is the new story without looking at the book's copyright info.
Secondly, for a long time it was hard to tell if a particular book was part of a series or where it went in a series. They have actually improved quite a bit in this area recently.