So far I know are the really old seme blades look like Timo described and older ones have a central rib like the one in question and from the middle of the 20th centry were used flat blades from recycled machete blades or other material. But like the others said, the colour look really fresh, early collected in it's life or recent, the only two possibilities IMVHO.
The lion spear look like it has some good age.
Regards,
Detlef