Nope! Everyone just knows that "John Mandrake" is actually a non-Magus Janus / Nathaniel. 
Although: kudos, Katie, for recognizing it!
Nope! You and Katie are literally the only two people I know of who recognize that. In my experience, NOBODY knows who "John Mandrake" is, period.
Explain your obscure references ahead of time, MANG! Lest you be called a hipster!

Seriously though, not everybody reads/watches the same stuff, I would say it's safe to assume 99% of Compendiumites aren't intimately familiar with anything but Chrono stuff, Dr Who (that's still a stretch), and Sherlock (a waaaay bigger stretch, there's not even time travel). That's not to say that anyone's stupid, but you can't assume we just
know.