This orchestra entity of "Northwest Sinfonia" is interesting because it seems to be variable in terms of size and performing players, based on the particular scope/budget needs of the game audio.
Simon James is the Contractor and apparently will determine which location venue to record in and will then hire of any number of individual session players to meet the project's needs.
http://www.simonjamesmusic.com/frameset.html
While Northwest Sinfonia has been credited for performing in dozens upon dozens of video games, this fictitious group name could be considered just an Alias for Simon James (the contractor).