Of course they can
As they are still in geographical context if not chronological.
But first you have to get rid of images of Time Team, archaeological surveys and rescue archaeology etc, on a properly planned dig only the thinnest layer of soil is discarded with techniques from sieving to floatation being used to find items down to the size of pollen.
Individually topsoil finds don't in themselves tell us anything other than they have been lost or discarded, one Roman coin for instance only proves it's existence and could equally have got there via a childs coin collection 20 years ago as it could from a passing Romano-Brit 2000 years ago but as your example shows an accumulation does add massive weight to a sites heritage.
One thing though, the Vikings as we all know were great seafarers and the existence of Persian, Arabic, Byzantine and even Russian coins in viking hoards is not uncommon and so the coins alone doesn't prove trade with these far flung places, only the item that these coins bought would prove that