--listen --tail with a large number only getting a small number of messages

I'm using a command like this:

```shell
matrix-commander \
--import-keys ../element-keys.txt "secret password" \
--room '!blahblah:matrix.org' \
--tail 1000000 \
--listen tail \
--listen-self \
--output json > chatlog.json
```

When I do this, I get about 1000 messages reaching back about a month. But I know that the room has far more messages than that. Increasing the value given to `--tail` doesn't change anything?

Am I doing something wrong? Is there some other way to say "get all the messages all the way back to room creation"?