We have always played it safe and had a wills for both countries. US assets on US will and Mexican assets on MX will. And yes, after that many years have passed I would get new US wills drawn up. Rules and laws change. Also, depending on the state you may need to have the US wills notarized and witnessed. Years back a Texas based will had to be filed with the state somehow. They don’t do that now. I email our TX attorney every few years to say hello and see if laws have changed and we need to update things. But then, I’m not retentive, I just like things tidy!