Who are "they" - Transport Scotland or Abellio? In either case, I still feel that it's a bit of a push to try and pin "more rather than less" blame on them - they aren't the rolling stock design experts, so why should it fall to them to spot that the curved windscreen could cause problems down the line? They're responsible for things like specification, financing, and carrying out due diligence, but expecting them to check the design for what is a fairly small thing like the shape of the windscreen is ridiculous IMO.
Further to that, the design at the stage of contract awards and signing will have still been very much up in the air and they'll have had a couple of different variations on it, no doubt. It is also worth noting that
DCA-Design only did the (interior) Cab design in "2016" a short while after the first bodyshell started appearing at the end of January 2016, which should give some idea of when things were getting finalised.