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In the Vibhaṅga to BuPj 2 (pli-tv-bu-vb-pj2) the definitions section defines gāmūpacāro… a term that is not used in the rule or, indeed, anywhere else in that Vibhaṅga. Why? Why are they going out of their way to define an unused term? Is the redactor of the Vibhaṅga trying to add this term to the rule?
Your thoughts Ajahn @Brahmali ? 
Hi Venerable, thanks for making this obvious point, which had completely overlooked! I think the reason might have to do with how gāma and arañña came to be understood, presumably after bhikkhu pārājika 2 was laid down. What we see is that arañña comes to mean any place more than five hundred bow lengths from the nearest house., e.g., in the Vibhaṅga to NP 28. Once this definition became established, pārājika 2 would no longer cover all case of theft, that is, if you stole something that was outside a village but within a distance of 500 bow lengths, you would arguably not be pārājika. And so I suspect the Vibhaṅga adds the terms gāmūpacāra, “the vicinity of the village”, to cover such cases of theft, presumably on the assumption that the rule is meant to cover all instances of theft. Personally I think this is a reasonable supposition.
Thanks, Bhante!
That makes sense to me and seems like the most likely reason.
It is interesting how in trying to be so conservative (e.g. by redefining arañña so narrowly) the Vibangha created entirely new problems like this one that it then had to solve in … creative ways.
Thankfully they also left the rule as it was, so we can retrace their steps. 
Yes, the law of unintended consequences. Every time we interpret, we create problems down the line. It’s so useful to keep this in mind. Yet we have no alternative but to interpret the texts.
Right. There are a lot of pointers to suppose the early assemblers of the Canonical material were conservative, starting with the contents of the suttas, which declare that the suttas should be remembered as they were taught. (E.g. DN 29.) It is this conservatism, combined with all sorts of other evidence, that makes it quite clear to me that we still possess the word of the Buddha, if not verbatim, at least in essence.