I found that in the group that I was DLing there were a fair number of deleted messages. What I think might be going on is this:
When you set PG Offline to download, say, 300 messages, it seems to keep downloading until it actually gets 300 valid messages -- meaning that any invalid/deleted message numbers don't count against the DL counter, and you wind up pounding Yahoo for that many extra times.
For example, I found that by subtracting the highest downloaded message in one "DL block" versus the highest from the previous block, there were actually more DL attempts (including nonexistent messages) than the DL limit said: with the DL limit set to 300, I had 328 and 322 DL attempts (and I was getting locked out), then with the limit reduced to 250, it was 277 and 261 (and I no longer got locked out).
For groups with lots of deleted or unavailable messages, this might be pushing Yahoo to cut us off sooner than it otherwise would? Worth a thought, anyway.
So for the record, my current settings are now 250 messages, with a 65-minute wait. I completed my 19,000 message group with these settings.
Pres