Donald,
The downside is that once you start the new group, I'm not sure what
happens if you still try to transfer the old messages from Yahoo after
new conversations have started.
The copied messages get assigned message numbers after the current messages, and possibly intermingled with ongoing postings.
This is not a big problem because the copied messages retain their original posting dates, so they appear in the "right" place in topics / messages lists (which are chronologically sorted).
Shal
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