Rule of thumb (at least the last few years) is that they come out in an anthology within a week or so of the novel that comes out at the end of the year. Until last year, that had been November; last year was September (which is good, it balances out the February novel timing a little better).
Then every once in awhile, 3 or so of the short story/novellas get packaged together into another 'book' -- you gotta be careful of those, they end up getting a new title overall so it's easy to be fooled initially thinking there's a new In Death novel out when it's just a compilation; the description usually gives it away....that, and the bad ratings from the people who DON'T pay attention....

They're fine to get if you didn't already get them in the anthology or just want to have them all-in-one without the other unrelated stories or whatever, just good to be aware of what you're getting.
