Something fundamental - how nov works

[Harry Putnam <reader@newsguy.com>]

I thought I sort of understood nov and how it worked but apparently
there is a large hole in my understanding.  I had assumed that if nov
were generated with nnml-generate-nov-databases-1 on a certain group.

That the messages in that group would become visible to gnus even if I
had copied them there behind gnus back, from the command line. Long
as they were legal nnml messages.

For example:
Create nnml group with G m 

Then copy several messages from some other nnml group there, giving
them arbitrary numbers. (from the command line)

If I run nnml-g-n-d-1 on that group some of the messages become
visible but not all.  However if I enter the group and press j
<NUMBER> using numbers of messages that do not appear, they are pulled
up by there number.  The nov file contains information about them yet
they are invisible to gnus.

What is at work here?  Apparently some stuff is written to messages
coming into a group by gnus, like the `X-From-Line' thing and maybe
`Xref' and `Lines'.  Not clear if that has to be there and be accurate
or not.

More example:

I've created an nnml group, copied 3 messages there from another nnml
group (from command line)  I've numbered them 2 4 6.

After running nnml-g-n-db-1 on that group gnus sees two of them 2,4.

No matter what I do 6 isn't visible to gnus.  It is in the nov file
though.  So apparently some other condition is not being met here.

I'm writing a little shell script that writes a certain kind of file
to a gnus nnml directory.  What must I do for gnus to see these
messages?

My script gives the message headers and body that look like:

X-From-Line: reader@reader.local.lan Sat Nov 24 18:40:59 PST 2001
From: 1124184059@reader
To: reader@reader
Subject: start the coffee later
Date: Sat Nov 24 18:40:59 PST 2001

get to it 
or whatever bla bla