In doing a translation, I have come across a date which has the character ヨ written in brackets after the year. I found some more cases of the same usage in what seem to be legal texts, but I still can't figure out what they mean of how to translate them. Does anyone have some insight? Do I even need to translate them?
The characters in brackets after the year are a special form of code which identifies a legal case as belonging to a particular category. The ヨ which you mention indicates that the case is a civil affairs case at a district court.
A more detailed list of these 事件記録符号 (case record codes) is available here: http://home.hiroshima-u.ac.jp/hirano/nyumon/fugo2005.htm
