[glhaynes]

I'm pretty sure actually that they don't do it when it gets to 20,000 docs (and thus we pay a bit extra for postage/materials than we might otherwise have to), exactly for the same reason you think so. But that's the adamant claim of those from whom requirements are gathered. It'll take me 5 minutes to implement the filter function to make this happen -- far less time than it'd take for me to sit down with them and have them prove that they actually do this operation. So I haven't pressed the issue.

I know for a fact that they do do it on smaller batches, though. It takes a lot of room, as you can imagine!