Showing Complete Active Threads

[Rolleston]

Such a simple thing this, but I'm struggling to find a way to do it:
I would like to see in the summary buffer the whole of each thread 
in which each new message appears. That includes any messages I've
already read in that thread. In other words, if a thread is active,
I want to see it all. If it's inactive, I want to see none of it.

I've tried (setq gnus-fetch-old-headers 1000), but it doesn't work,
even for small threads in which all the messages are very recent and 
are available. The message summary lines do not appear for messages
that have been read before. I can type A R to get parent headers, but 
it's tedious to do that for each new summary line within a thread, and, 
in any case, I'm not sure if it will reconstruct the whole thread, 
rather than just the line of ancestry up to the root.

Any help with this would be much appreciated,

Thanks,

R.