Geez, I can´t believe this is happening with NP... although it´s not a major, catastrophic issue.
The statement "they rather cut them too long than too short" really sounds more like "we had an issue during the manufacturing process". I concur with Harrow... there must have been an issue with tools and/or fixtures in the factory.
Besides, isn´t the threaded batten adjuster (the one he removes prior to cutting) precisely to allow extending the length of the batten if need be?... I think it can extend it up to 15 or even 20 mm... This doesn´t support his statement that they rather cut them a bit longer, as the way it´s conceived with the adjuster, it should be a bit shorter, understanding that by "a bit" he means 5-10 mm.
Anyway, I guess even the big players in this industry make mistakes