Certain factions can buy Generic DC's, but being generic, they're not the only factions that can purchase them.
So for example, the X-wing DC, which is not a generic, is currently owned by the New Republic, who are the only faction who can make them.
The N-1 Starfighter however is a Generic DC, meaning that any production faction can build them as long as they purchase the DC.
It gives new production factions the ability to make a few ships, items, etc. Which is much better than how it used to be before the generic DC's were introduced, where production factions got nothing.