You're right, that's one weird detail from the novel that all adaptation except this version skipped afaik.
It's funny to see how this version stays true to the novel in a weird way XD
There's similar case with the old adaptation of "Kaze yo, Banri wo Kake yo", a novel by Yoshiki Tanaka based on Sui Dynasty's expedition to Korea. The translator choose to using Chinese & Korean pronouncation of all the names than Japanese pronouncation.
Your welcome. Samura Hiroaki is one of my favorite mangaka and I really want to work on this oneshot collection. Hopefully we can work on this until last oneshot.