I'm pretty sure they were made from the mid 80's to the early 00's. That would make them vintage USA lamps. Up until the mid 90's they had screw-top caps. Those were replaced with a bottle cap and a lid over that to match the base.
The image below shows the Silver Century with screw-tops.
Thank you so much for the pic and the information. So nice of you to take the time to reply!
Have a Great Day!