Can silver be sterling if not marked sterling?

The work apparently originates from the 12th and 13th centuries, coming from the Old English "stiere", meaning "strong, firm, immovable". I hope this helpsRgds

yes

In 1904 the Silver had to be marked with the .925 in an oval shape, with the Brittania Standard silver mark being .9584 in an oval shape. In 1973, the new Hallmarking Act dropped the decimal ( . )...

In the US, sterling silver is 0.925 pure silver. It is assayed and hallmarked to show this. Different countries use different hallmarking systems. The remaining 0.075 is usually copper.

Not exactly. Sterling silver is an alloy of silver and is made up of 92.5% silver and 7.5% of another metal, usually copper. Adding copper/the other metal strengthens the object.