Well, the earilest Silver Stars were issued at the same time as the Purple Heart, which was in 1932. I've seen Silver Stars issued to WW1 vets up into the 1960's. I'm sure there are some even later than that. Whenever the vet put in for it, the engraving will be of the style of the time. For example, the 1932 through WW2 will be hand engraved, with 3-4 different styles of hand engraving. All came out of Philadelphia. Post WW2 will have machine engraving.
Hope this helps some,
John