Forget the marks (sorry, Cyberman). They are only a convenience, and a modest one at that.
All you care is that the crank is at TDC and each cam has the marks matched when the belt tightens up. If they're off, they have to be at least one whole tooth off, so it is very easy to tell.
The first thing you'll do once you tighten up the belt is turn the crank two revolutions to make sure everything is still lined up. The marks on the belt won't be anywhere near the marks on the sprockets then. (Even if you turn the crank to bring the marks all the way around, they STILL won't line up where they started from -- this is by design.)
Note that distributor (ignition) timing is set separately, after you get the belt on (the belt sets cam timing). Even if you carefully follow the FSM it is not too hard to get the distributor off one tooth. Easy to tell; you'll have about 27º of timing error.