Interesting. The update Sept 2017 covered minor differences associated with my '18 GS Rallye, such as rear peg changes needed for adventure cases install.
Jet is right however that even the older BMW RSD DVD covers most of what you would need.
For example, take a look at the screen shot of this page from BMW Motorad site where you can download the riders manuals for most bikes. Heres the link to that page:
I find the riders manual has quite a few good service instructions on its own, (see the second screenshot which is from the latest 2017 GSA manual table of contents). On the bottom right of the download page, the links for different riders manuals imply the differences by year and by VIN that translate into model code, e.g. A02 and A22 vs A21 (USA model).
On it on the top right of the download page, you see they ask for VIN. I would recommend you have your VIN decoded for both the RSD and riders manual which ask for specific model code and year. Can to that here:
Bottom right you see all the available GSAdventure (USA) manuals, where the primary rider's manual list models "Aug 2014 onward", "Aug 15 onward", "Aug 16 onward", and then stops at "Aug 2017 onward" and "with SA XBABA Connectivity"; these last 2 are separate links. It also lists supplement for Rallye. So, depending on whether you've the TFT (aka Connectivity) or Rallye you will want an RSD that is updated to cover those elements; updates are downloadable after you purchase the RSD. As mentioned, the RSD my dealer sold me in Oct 2017 did not cover my 2018 GS Rallye, but a subsequent downloaded update of RSD (in January 2018) covered the same features as the GS supplement riders manual: the cosmetics and different options installable and their implications for servicing later. I am surprised the current 2018 GSA is not already out there as an update.
Lastly, if you just bought this bike, you can get a discount from your dealer for the RSD. Mine was 20% off because I asked for it within a month or two after buying the bike. I think standard is 15% off all parts bought within a month of your bike purchase.
Best of luck.