So the silver Ikes stopped in 1974 (reason to me yet unknown) and the clad SBAs started in 1979. It would have been nice of course if they released a 40% SBA. Or in 1999 a 90% one...Sheesh make something to spur SBA interest... Here is some interesting information: https://www.jmbullion.com/ultimate-guide-to-40-silver-coins/
As far as I can remember, being around at the time, there was never any discussion of creating a silver version in either 40 or 90 percent.
To answer your question you first have to be aware of and remember the process. Before there can ever be any discussion about such things, beyond personal ruminations anyway, a member of Congress has to first submit the idea in a bill. And after that, and only then, is there ever any real discussion about the matter.
