I tried to be careful: It only means some part of the products were made in Japan by Taiyo Yuden.
And it's not TY that sells some TY media. TY sells to OEM buyers and from there TY has less degee of control.
If there's Taiyo Yuden in your hometown, there's SKC in Chon An, 40-min by KTX rail from Yongsan Station. SKC invites lots of consumers and reporters there just like Samsung and LG do often. They usually stay from morning to 5-6 PM in the factory looking at the production lines with occasional conversations with the engineers and managers, but nobody actually knows everything about their deals with Hitachi-Maxell or how their "trash-degree" SKC media meant for destruction are sold on a few retail online stores or how they could influence the government to make 56% tax on all imported CD media possible.
Let's suppose there are two, not one, companies that import media from TY Japan to South Korea, one based in Seoul and the other in Busan. The first has been longer in the market and has a larger market share but suddenly attacks the latter among the dealer community and enthusiast consumers and testify the TY media from them are not TY but their own products are real TV even though they admit that theirs are not 100% made by TY either. So the wounded competitor that brings TY media market prices down wants to say something to alarmed consumers and small resellers and starts talking more. The small war ended in basically the first company achieving more complete monopoly of the TY Japan source, but they still couldn't prevent a third company from importing from the Verbatim-end of Mitsubishi (bypassing the importers of Mitsubishi-branded Mitsubishi media) and TY/Mitsubishi media.
I hardly suspected those would have any different MID or serial numbers, but none of what I have said has anything to do with theory or assumptions.
Even packaging is an important manufacturing process especially with DVD recordable media. Adding something onto those is even more important.