I would posit that some specific DNA strains (most notably those of the mentats) would be genetically adaptable to have Sapho work on them differently. The expanded writings about sapho having a cure that must be "survived" while not in the original certainly may be true for those who are not genetically comparable like many mentats are. But it is also important to note that the mentats are genetically comparable because they will themselves to change/adapt.
Non-Universal results would make it seem to the outside Dune world as being "questionable" in the efficacy of Sapho. Being addicted to Sapho may even be a side effect that means lack of genetic comparability.
Additionally, the Mentats mantra "It is by will alone" supports the idea and claim that they will themselves to adapt. A mantra that constantly reminds them they are not randomly beneficiaries of sapho juice. It is also why so much of the landsraad treats mentats as a "religion".
This theme is also held by the bene gesserit, but they have a different philosophy to how they approach the end result. The goal of bith schools of thought, (Mentat and bene geserit) is the Creation of the super being. The mentats through self-will, the bene gesserit through a secret breeding program.
The bene gesserit got to the end goal first with Paul Atradies. But they had to fill the gap in lost genetics (due to war) by joining house harkonnin and Atradies. That link was in jessica who was reveled to be the baron harkonins biological daughter from his early life before he strictly preferred young boys.
The Spice, was the step trigger that initially opened paul's Consciousness was just the pre-step to the Water of Life. An opening of mind and body so great that it was only effectively used by bene gesserit, until Paul.
The irony of the story is that both schools were right, but neither had a complete view. It took genetics through breeding AND self will to create the Super Being, the quisach haderach. By the time he was created, he was not controllable by either group, (much to their dismay) and worse, he was in control of the Spice itself.
A lesson to us about the possibility that the answers of our greatest struggles and dreams may have answers that are more than binary (yes/no).