If true, RS, why can't I use my free play at other Boyd properties?

Or, are Sam's Town and Suncoast the only two that are linked,

Frankly I think I just happened to have gotten a free buffet at the Suncoast free drawing, and that's all it was. Gee, it was just a free buffet for ONE person. I think they gave it thinking I'd bring along a paying customer with me.