It's not unusual to come across Hamilton watches that were intended for markets outside the US. One clue is you can't find them in the Hamilton catalogs. Another could be markings on the watch itself. Some models were both, like the 1964 Dateline A-578. It's part of the Estoril line and there are several variants that were marketed outside the US.
Estoril is a seaside region in Portugal - considered the Portuguese Riviera. The Dateline A-578 was marketed in the US but additional versions in solid gold and gold electroplate were also offered outside the US.
The ads I found online show there are a couple of potential original bracelet designs and it's interesting to note that the font used for Estoril on the dial can vary - presumably by year or market.