balancerider is spot on there, in amongst the option codes at the end of the build list there are flags for the factory to make special builds, the 991 code is one of those.
The term "pre-series control" means it is a test vehicle that is being built for the purpose of testing and homologating a new function, or combination of functions on the vehicle. This will be used by the engineers in Munich for a period of time, which may not even involve driving it, to carry out the required tests to make sure everything is working as it should before the function can be made available to order on standard production cars. After the tests are completed the cars are offered to various markets, like NZ, for sale and if not sold are recycled (there is a cool video of this process on the Tube). And yes, these cars do often get built with funky options, like 330d wagons that have full Professional Navigation but no auto lights or wipers. Nothing wrong with them, still good cars, just different to NZ specs.
Quite a few of these vehicles have ended up in NZ over the years as we are one of only a few RHD markets, and we have very loose import controls compared to most of the others.
For Press cars there is a seperate option code which is 902, there are also codes for Show cars, that is cars which are to be presented at motor shows or other exhibitions around the world, and various others. There are many rumours about the 902 Press cars having different engine tunes to give more power and better drive, etc so the journalists give better reviews! No idea if this is true or not.