I played yesterday and I suspected the Rebel Base was on Tatooine. The SYSTEM was empty, so I constructed a Death Star there. The card stated that the system must contain no rebel units. My opponent said "Ummm, but it DOES contain rebel units"...
This lead to some confusion. Was I able to begin construction of a Death Star on a remote system, IF that system turned out to be the rebel base (and simply hadn't been revealed yet?).
We decided that the rules implied that this was legal, so construction began. My friend however, had accidentally given away the location of the rebel base. (I was heading that way ANYHOW, because I suspected).
Did we play it correctly?