Curious. The card in my set doesn't say anything like that. It says:
"Treated as a minor company in the initial auction. May be sold to Open Market and bought from the Open Market at face value during a Stock Round."
My rulebook ("Version 1.0, 4 October 2010", which is the latest version available for download from the publishers website) says essentially the same thing, slightly expanded, in section 3.2.5. Is section "3.2.5 The Guillaume-Luxembourg" in your rule book? If it is different from what the card says, keep in mind section 9, which includes: "In the event of conflict between the official rules and any components, the rules take precedence."