Hmm, ok, my theory:
In-system jumps are basically the same as inter-system jumps, they rely on existing 'wormhole' or subspace tunnels. So, you have to use your Nav subsystem, find a node that is stable enough to lock onto, that also has an egress point to close to your destination. Notice that wings warp in next to each other... ergo, they use the same subspace tunnel, but open individual portals by which they access them. Once found, your subspace drive stabilizes and opens the node, and then your engines push you into the node (which is why, without engines, you can't jump).
Inter-system jumps rely on much larger and much more stable jump nodes that cannot possibly be stabilized by a ship (unless perhaps it is Shivan tech); therefore, they have to be stable enough to use without stabilizing; you only have to open one end and enter it.
Also perhaps affecting this is that if you notice, the Knossos stabilizes a jump node, so much that when it is destroyed, the node still exists... or that was a side effect of the destruction. So, if one ship stabilizes a node for in-system jumps and uses it, it should remain open for awhile, and other ships can use it too. If it collapses, the other ship just has to lock onto another node that opens into the same vicinity. Just my theory... basically, in-system nodes form and collapse all the time, and jump drives lock onto and stabilize them for use by a ship. Inter-system nodes are much bigger, and form and collapse at a slower rate, given their size. (This solves the mystery nodes to Sol, I think... the other ones were close to collapse, but naturally would have lasted a long time, but the Lucy's blowing up half in subspace affected them, because they open into the same vicinity as the node the Lucy used, and the Lucy was half-in, half-out.)
