I appreciate you taking the time to point this out.
From my perspective as the consumer, I see something that looks slightly off and wonder how this "obvious" "problem" (both words intentionally in quotes, they may be neither depending on your perspective or one or the other) couldn't have been caught in the development stage.
My perspective is clouded by a certain degree of ignorance.
For example, I look at the incorrectly sized tabbards and think, "If I were creating the prototype for this, how could I miss the length/width if I spent 5 minutes comparing it to these reference photographs?" And if I were to see the problem, I can't see it taking very long to fix (make a new estimate of length, cut it, test it). At most a day or two?
I also write software for a living. While I'm not directly equating the two jobs, I think there's likely to be a similarity between schedules and deadlines. I'm used to making compromises between perfection and "good enough" so I can understand that perspective as well. Does that factor into it as well and how or does delays at the development/prototype stage affect production? For example, would say, a day's delay of preparing the prototyping/pattering the costumes affect the actual production by say, weeks or months?
(If it does, from my perspective since I wait so long between the pre-order to actual product, a week or two delay is completely unimportant to me if it would mean ganing more accuracy)
Am I close to the mark as to how these "obvious" "problems" can happen? If not, can you explain how they do happen?
I guess its just tradition 
