More important than were the glass was made is who made the lenses, and most lenses are not made by the same people who made the glass for them. The Japanese, Germans, and Americans are fully capable of making equal quality glass. Also, just because it is Schott glass does not mean the glass was made in Germany, they have production in several countries, and it also doesn't mean Schott actually did the grinding and polishing as they probably did not. But good glass can make a bad lens if the lens manufacturer does not do their job (and I have seen bad, and superb, lenses from Germany and Japan along with other places of origin), or if the lens designer doesn't. You can't tell where the glass or a lens was made by how clear it all looks. "Assembled in ..." generally means parts were not made there, which most likely means Asia but there are certainly other excellent lens manufacturers in Europe. But for the HD5 I do not know where the glass or lenses came from, so you may be right.
Justin