Battle of Deneb (2335)
During the first Great War, a Shivan fleet centered around the SD Lucifer and the destroyer SD Eva made use of an unknown jump node to bypass the GTA blockade in Antares and reach Deneb. After Alpha 1 made a reconnaissance of the Shivan arrival in Deneb, the Shivan battle group and a Terran/Vasudan fleet, including the GTD Galatea, GTD Legion and PVD Hope, engaged in battle. The FS2 intro cutscene and two FS1 missions, Evangelist and Doomsday, show the the Battle of Deneb (2335) from different perspectives.
The FS1 failure debrief for Evangelist claims that there are only two Shivan destroyers in the system, the Eva and the Lucifer, but the player destroys the Eva if he successfully completes Evangelist. However, the FS2 cutscene clearly shows a Shivan SD Demon-class destroyer present after the Galatea has been destroyed. As the Eva is implied to be the only Shivan Demon-class destroyer in the system, this is an inconsistency unless we assume that either the Eva was not destroyed or another Shivan SD Demon arrived in-system during the battle. Also, the FS2 intro cutscene shows many cruisers and destroyers present during the Battle of Deneb probably after the destruction of the Galatea, and the destruction of another Terran GTD Orion class destroyer, presumably the GTD Legion.
For more information on the introduction cutscene's inconsistencies, see the FreeSpace Trivia page.