"Advanced Find" in Outlook 2007 is not finding all email messages
which match the criteria. It finds between 30 and 200 and then stops.
I then have to work with those (e.g., delete them) and then click
"Find Now" again to find another batch, dozens of times!

What is wrong? How do I fix this and find all messages that match the
criteria?

My typical application is to split the entire contents of my .pst
files by date. Do do this I make a copy of the file. In one I delete
all messages older than the cutoff date (e.g., 1/1/2007), and in the
other I delete all messages younger than or equal to that date.
Outlook XP (2002) was able to find a couple of thousands all at once.
(FYI - I think my files are structured as legacy Outlook campatibilty
type, not the latest Outlook 2007 type.)

Why is Outlook 2007 not finding all files and how can it be fixed?

Craig in NJ