Hello.
The "A" is just a pseudo mark, not a date mark.
A or A1 are often used on silverplate to imply high quality or thickness of the plating.
The next three marks were used by E. & J. Bass. Check here:
http://www.925-1000.com/silverplate_B.html" onclick="window.open(this.href);return false;
We often see the words "Sheffield" or "Sheffield Reproduction" on American silverplate.
Generally used on silver over copper pieces.
704 is a catalog or pattern number.
Pat.