It varies from pressing plant to pressing plant. I made a few records in the late 80's/early 90's and the number of test presses we received varied between 3 and 20. Some pressing plants would accept an order for 1 copy, while others wouldn't accept orders smaller than 500 copies.
 
Peter
 
 
Date: Thu, 01 Mar 2012 08:44:10 +0200
From: Antti Lavio <antti.lavio@possu.org>
To: "All bound for Mu-Mu Land." <klf@mailman.xmission.com>
Subject: Re: [KLF] KLF 010-IT
Message-ID: <4F4F1ABA.80706@possu.org>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

On 1.3.2012 0:52, Ross Jarvis wrote:

> The question is: How rare?
>
> As with almost every collectable item, I suppose it comes down to how
> many were initially available

It's impossible to say without knowing exact amount of records pressed.
It's bit hard to believe these "only 3 pressed" claims, as I don't
believe that any pressing plant would do only 3, even if it was a test
press.

BTW, there's a good article about vinyl pressing at

http://www.crimson-ceremony.net/pr3/pressingplants/intro_tp.html
http://www.crimson-ceremony.net/pr3/pressingplants/intro_vinyl.html

It also mentions Orlake and MPO, which KLF also used.