One thing that's striking me about the class 7xx, which was presumably introduced recently because they were running out of spare 3xx classes to use, is the rather bizarre numbering scheme.
First one was, IIRC, the 700 - fair enough. However since then the numbering seems to have been almost haphazard and random. Logic might dictate that they would either be numbered in chronological order (so that the second class to be introduced would be the 701, then the 702, then the 703 etc - similar to how the AC 3xxs are numbered, at least up to the 325) or some sort of systematic numbering as was done on the southern (so that 700-09 are manufacturer A, 710-19 manufacturer B, and so on).
Instead the numbering seems almost like the output of a random number generator. Maybe there are patterns, but they are not obvious (why did the 707 come before the 701, for instance?) It also begs the question, given that the 7xx has ended up with the same haphazard patterns as the later 3xx (it was logical up to and including the class 325, then went a bit strange) any new units are going to have to use the unclaimed numbers. If that is the case, there are plenty of unclaimed numbers in the 3xx range (starting, I think, with 326-329) so why didn't they just use up all the 3xx before moving onto the 7xx?
First one was, IIRC, the 700 - fair enough. However since then the numbering seems to have been almost haphazard and random. Logic might dictate that they would either be numbered in chronological order (so that the second class to be introduced would be the 701, then the 702, then the 703 etc - similar to how the AC 3xxs are numbered, at least up to the 325) or some sort of systematic numbering as was done on the southern (so that 700-09 are manufacturer A, 710-19 manufacturer B, and so on).
Instead the numbering seems almost like the output of a random number generator. Maybe there are patterns, but they are not obvious (why did the 707 come before the 701, for instance?) It also begs the question, given that the 7xx has ended up with the same haphazard patterns as the later 3xx (it was logical up to and including the class 325, then went a bit strange) any new units are going to have to use the unclaimed numbers. If that is the case, there are plenty of unclaimed numbers in the 3xx range (starting, I think, with 326-329) so why didn't they just use up all the 3xx before moving onto the 7xx?