King George III Duty mark only

Hi everyone,
I was wondering if a King George duty mark would be sufficient to identify something as sterling even if there are no other apparent hallmarks, My reasoning is that I am under the impression that this duty mark preceded the advent of silver plating. In addition, why would there be a duty tax paid for a base metal which seems to leave sterling as the only remaining option. Perhaps the other marks were there but over the past couple of hundred years they got rubbed away?
Thanks in advance for any thoughts on the matter,

No, it is not sufficient. Is it a genuine duty mark? or just a look-alike. If you can see the duty mark then why not the other parts of the hallmark which would have been stamped at the same time and with the same level of force? A picture might help.


Thanks for your insights, Phil.