Question about numbering of internal nodes in circuit diagrams when one circuit element has more than 1 internal node

I have the following circuit diagram that I’ve added labels for the internal nodes to using outside sources. I understand what an internal node is, however what I’m confused about is– for example– E1 has 2 wires connected to another circuit element, so they’re both internal nodes, but how do I distinguish which is n1? Or is this completely arbitrary?

And why is n2 after E4 here, is it because it has to follow the flow of the circuit?

Sorry for the noob question, my book doesn’t explain this (at least so I’ve read, I could be missing it).
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