Yes, such things are often outdated, but the availability of different memory chips does not change existing hardware. The MC really doesn't support it, there is no way to change anything about that...
I believe there were other chips at the time that supported more than 8 GB (i7-9xxM perhaps), but these are a different die (Clarksdale quad cores, ie. high end mobile chips that are selected desktop chips).
The difference is that with the one DS we know it's accurate because anything beyond 2 Gb simply doesn't work. So that DS is accurate. On the other hand we know that with Clarksdale more than 2 Gb does, in fact, work, just like they work on Lynnfield. As one would expect, it's the same silicon after all.
If you'd excuse me now, I believe my work here is done ;)
The point is that the datasheet is now inaccurate. This happened before with 2Gbit DDR3 and Intel had to update the datasheet for the Mobile 4 Series chipsets.
I believe there were other chips at the time that supported more than 8 GB (i7-9xxM perhaps), but these are a different die (Clarksdale quad cores, ie. high end mobile chips that are selected desktop chips).