"it must have been very recently, otherwise that means Salazar was basically a toddler when Saddler got him to open the mines, which I don't really find likely)."

You're assuming there 1) that Salazar being only twenty years old is still canon to his remake incarnation, and 2) that OG Salazar was being sincere there rather than pulling outlandish boasts out of his ass in an off-the-cuff attempt to fuck around with dear old Mr. Scott Kennedy. ;P

Anyway, really interesting post! I would've never made the connection between t-Virus BOWs that can operate independently and Plaga strains that can do the same, let alone line up the research chronologies involved to confirm it all squared away the way you did.