In my experience, not all were marked. Also in regards to stainless, when looking for replacements for missing instruments, be aware that while the patterns of many instruments may not have changed, small style details may have. In other words, a Mayo pattern scissors from 1941 looks different than the same pattern from 1991. So since instruments don't have dates on them, an early appearing unmarked instrument is more likely to be correct than a modern looking one marked "Med Dept USA"
That make sense?