I showed the OVA episode during my Violet Evergarden Marathon in my theater back in July, in the order it takes place - it is the perfect Episode 4.5 to fill in a lot of Violet's letter-writing skill development, between her trip to Iris's hometown and the Princess/Prince Love Letters episodes. I think the anime staff saw that they had too big of a missing gap at that point in the series, and rectified it with the Extra Episode. I'm anxious to compare the Netflix translations to the Komorabi fansub, which was the best we had to work with up to this point.