Hard to know what the heretics quote means- however, it must be pointed out, the heretics universe was quite different from the Dune, DM-CofD, or even GEOD universe in terms of travel- the scattering just had to of fucked everything up in terms of reliability to the guild- and all those No-Ships everywhere couldn't of been too thrilling either- a guild ship is very large, packed with goods of every sorts, and thus very vulnerable.
It's really hard to imagine how they resolved these issues- many, many directions they could of gone that was unspoken. It's easy to see how many of these systems we can all brainstorm can apply to stages of navigators. Is it skill-level related, or specialization, endurance, genetics, routes traveled, tactical and strategic concerns your trained for (like TEG, the BG general- something they never had needed in the past).
Very, very hard to say. It's impossible to come upon a authoritative consensus on this by trying to figure it out- Frank didn't say much, and we have so very little to grasp at. We do however know the universe, and everyone in it, changed ALOT.