Not sure if I interpret "within an entire family" correctly, but the online specs for the 820QM are clearly wrong
Yes, this statement is very blurry - I thought about artificial memory limitations like ones in C2000 Atom server series - there are almost identical models (C2530 and C2550 for example) which has different maximum amount of RAM. For Clarksfield web part of ARK is obviously wrong, as official third-parties like Lenovo stated 16G support, but datasheet is no better:
"One or two channels of DDR3 memory with a maximum of one SO-DIMM per channel"
which is certainly not related to widely used Clarksfield four-DIMM setup.
Definitely not worth it for this 7+ year old hardware (unless someone has a suitable scope and the knowledge already... the best scope I have access to is an Agilent MSO6104A but no idea where to even start - and no interposer obviously) but you seem to imply that the 8GB problem is an analogous one... do you think about the 16 GB problem as well?
I don`t think of this problem as of 'analogous', there`s simply not enough data to understand the problem. I have 720QM with 32G, but this laptop hardly could be called portable, perspective of having >8G of RAM in Arrandale laptops is brilliant. Regarding issue analysis, I suppose nothing much could be done with *scopes*, because data exchange violation seem not to be strict and/or large and it is impossible to catch this one in a sane time without proper bus analyzer. Speaking for Agilents, only 1690x chassis are capable to work with analyzer blades suitable for DDR3 analyzer, but they are somewhat pricey.