My table's answer
Your very precise momentum vector determines where you will end up, since that is distorted by the multiple moving masses in the system, the safest place to control that is the point where all the system's gravity distortion cancels out. (That's why advanced T3 Nav computers can handle a slip a bit further away from the actual zero point, and it is possible to slip arbitrarily with T4, thanks to advanced AI or quantum computers) You can initiate the slip from anywhere but you will probably end up in the middle of nowhere(literally) with no hope of calculating a route back. Even if you managed to end up somewhere useful, that slip would be impossible to replicate because the planets and other mass in the origin system will have moved and changed the original vector. That's why the slipknots are used. They are reliable and consistent.
So it is possible to go to any system from any slipknot, and we say you may pick your destination slipknot by taking double time for your calculation, or just accept to appear at a random knot at the destination. We also used the formula; Roll 4dF, 0:Your choice, +1-3: Zenith knot, -1-3: Nadir knot, ±4: Somewhere else in the system.
Some extra effects
Because the systems and galaxies are moving in relation to each other, the systems in a cluster get disconnected, and other systems may link up from time to time. This is a slow process, and it is a rare occurrence. Generations pass within a stable cluster, with legends about a "lost" system that was the home of the ancients once upon a time, or the news of strange explorers arriving from a newly linked system.
There are probably many other systems theoretically reachable through a slipknot, but the entry vector required is impractical or even impossible with available reaction engines. Or the heat buildup is so severe that the trip is not survivable.