It always makes editors suspicious when people evade direct questions, and conceal the information that is obviously required to give a good answer.
Without more information, the answer is always going to be "The Book of Submittal Procedures" -- one submittal per site.
If some other editor had more information and gave a different answer, ... you can go with it. But no editor can give you or your owner a guarantee: the editor who reviews the site may think differently; the community may reach a consensus that overrides both of them. The only thing you can HONESTLY tell the owner is that you will suggest the site, but there is no predicting if or when another listing will be added.
Telling the truth up front may save him getting angry with you later -- as other visitors here could confirm from experience.