The first DVDs are produced, and the team working on those re-creates the soundtracks. In some cases they use the GNP Crescendo as the source for the music, even though that source is inaccurate. In our scenario, Lights of Zetar is one of those cases....
Yes we can sync up the DVD or BluRay to the GNP, but that's just an historical artifact of how the DVD & BluRay releases were put together. It doesn't have anything to do with the completeness of the soundtrack box set. We're not using the right reference to identify cues.
This may be true, but it seems to me that this is somewhat over complicating the matter. A theory: the original Force Field cue was made as one standalone cue which had a proper 'end'. This was joined together with the Silvery Orbs cue during the editing process for WNMHGB. However, series 3 rolls around and the editors decide to use WNMHGB music in Zetar; they use the *original* unedited tapes, resulting in a decision to end the teaser with the original Force Field end in tact.
2012 rolls around and La La Land decide to recreate how the cues were edited in their originally intended episodes. Result: the end of Force Field is merged into Silvery Orbs as per the original episode it was intended for.