IANAL, but I believe you cannot put "(c) Your Name 2020" on Shakespeare's works in Japan and other countries. Their copyright acts protect the moral rights of authors[1][2]. So I think Zen's file headers would be violating the law in Japan and other countries.

[1] https://en.wikipedia.org/wiki/Moral_rights [2] http://www.japaneselawtranslation.go.jp/law/detail_main?id=2... (Copyright Act of Japan) Subsection 2 Moral Rights of Authors (Articles 18 to 20)