using (`gnus-summary-universal-argument')

[hput <hput3@fastmail.fm>]

It seems I'm unable to get the functionality the manual describes for
(`gnus-summary-universal-argument')

I position cursor at the top of a group of 5037 messages

then press `Alt-Shift-&' (`gnus-summary-universal-argument') which displays `M-&'.


then  press 'C-u 5037 J #'


Which the manual says will mark the next 5037 message with `%' the
gnus-agent-download mark

But instead it marks only 1 next message a few times as many as 3-4
but never any where close to 5037.

I continued to think I am doing something slightly wrong so tried it
many many times 

I've tried this many times today, did it slow and very careful.  But
no mater how slow and carefull I get only a few messages marked

Can anyone spot my blunder or misunderstanding?

Further, once I have manually marked a number of messages with
the `%' how to tell agent to go ahead and download them?

Doing C-h b on summary buffer and searching in many ways .... first
off finding all `gnus-agent ...' hits.   Checked for the word download, etc etc.
but not finding anthing promissing.

I seem to recall it might have something to do with pressing 'J j' but
that doesn't seem to change anything.

Let me explain that I once understood how to do all this and did so
many times 15 or so years ago,  but apparently some critical part has slid out of
my pea brain; a very aggravating experience that seems to occur more
often as I approach 80 yrs of age. 

Can anyone offer some advice or assistance?