Hmm. My immediate response to reading this was that it's a problem if the subgroup you belong to is determined by which research group analysed your sample! I guess that's not what he meant.
Different findings in different laboratories only suggest subgroups if those findings are incompatible with each other in terms of mechanism. I am not sure I have seen any such incompatibility. And the most likely reason for different labs finding different things that are incompatible is that none of the findings are solid. Suggesting subgroups is a popular way to explain away inconsistencies. There may well be subgroups but unless Younger can say something more specific this looks like wishful thinking to me.