The resquest mode is specific to the CI being published in the catalogue and not to the people who might be entitled to request it. The logic is that a request once entry will be shown until the service has been succesfully requested by an individual. When that person returns to the catalogue it will no longer be visible.
Still not 100% on this.
So the "Request Once" IS specific to a user for that particular CI.
So it must be checking existing requests for that user in the system to check if that CI is already requested?
Ah! I see what you mean. Yes, when the catalogue builds, it brings together a number of elements to decide on what to display. A existing link between the user and the request once service will mean it is not displayed.