What's so ambiguous about these certificates? It says "Enjoy a weekend night on us" and then specifies a second night free when staying any two weekend nights: Friday/Saturday, or Saturday/Sunday. [In parts of the world where Friday is the religious day, then Thursday/Friday constitutes a two-nightweekend stay.] I think this is another case of newbies not quite understanding the English men's club nature of Ambassador. It is different from FF programs, and its rules and operations are somewhat more genteel.

As for the point of the original post, I suppose wording it this way doesn't rule out staying three weekend nights, and still getting one of those three nights free.