My reading of it is that most people believe that Mal is completely 100% wave-free original, but if Mal has a biomod, he doesn't know if he has it or what it is himself. Some Fen do get biomodded and never know it, because the benefits are so slight they don't matter, or simply because they haven't actually been put in a situation that the effects actually become noticeable.
For instance, one might gain the ability to survive in vacuum for a significant amount of time (read: longer than 40-60 seconds), but since one doesn't as a general rule go tossing themselves out of open airlocks and hull breaches, it would go pretty much unnoticed bar an incident that does so for them.
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"You know how parents tell you everything's going to fine, but you know they're lying to make you feel better? Everything's going to be fine." - The Doctor
For instance, one might gain the ability to survive in vacuum for a significant amount of time (read: longer than 40-60 seconds), but since one doesn't as a general rule go tossing themselves out of open airlocks and hull breaches, it would go pretty much unnoticed bar an incident that does so for them.
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"You know how parents tell you everything's going to fine, but you know they're lying to make you feel better? Everything's going to be fine." - The Doctor