I just wanted to say the how and why the mint made the SMS coins would be just my opinon.
Not sure if I have read any official details, as far as the process or reason for making them.
What I was saying, "for a lot of effort", was having to replace the massive amount of coinage
that was being pulled out of circulation at that time. 90% silver coins were being saved
by many americans, also wheat back Lincoln cents were starting to be saved in larger numbers.
Most people I knew in the 60's and 70's were saving the silver coins, I still have some I saved.
Those coins had to be replaced.
Having to replace all that coinage, had to have some impact on how they put out mint and proof sets.
By 1968 they had the coin shortage caught up and were back to making what we consider regular mint
and proof sets.
I think along the lines of having to make a massive amount of bullion American Siver Eagles in 2009, costs collectors
having a proof
ASE for that year. I know, not the exact same reasons, but still a negative impact to collectors.