I would just like to point out that as part of Khan’s background, Marcus included that he was one of the nine survivors from Tarsus IV.  Now, that would be really weird considering it was acknowledged that there were nine survivors before Khan had his fake background as John Harrison.  But, what if Marcus took advantage of someone deleting their background on Tarsus in his medical file; it doesn’t say he was there so Marcus took the opportunity and gave the deleted information to Harrison.  But who would be smart enough to hack into a Starfleet database?  Who would be desperate enough to want to erase that part of his memory from official records?  It never happen… at least not to him.

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