Calfskin, the Zyns I talk about are NOT from 1999 - they are the classic 60/70/early 80s Zyns/Super Zyns/5 Stars. The ones from the period when everything else Premier/Olympic was made in England.
The newer ones could, like Olympics from that time, be from the far east or anywhere else.
I can´t and won´t try to explain your odd 404. I can just say that 404s are normally regarded as the same blanks as 505s with less hammering.
But if you really care about the composition of the bronze - why just look at it? Why not have it metallurgically investigated in a lab?
Oh - it costs.
Jon