Hi,
I'm sorry to disappoint you, but I don't think this is a high-grade blade or dagger. It is a classic, basic Chinese/Tibetan (possibly Mongolian) dagger, most likely produced in the mid- to late 20th century. The simple flat blade is consistent with the hilt and scabbard, so everything appears to match.
To answer your question, however, old sword blades were sometimes repurposed and reused to make daggers. South Indian katars, for example, occasionally incorporate recycled sword blades.