Well since dates are human concepts as well we can just state it is immigration date 00/00/0000. Are the months or days first? That’s up to you, haha. You make a good point, but you understand what I mean. If we consider immigration only being the integration into another state permanently then we would have to say we had mostly open immigration into the U.S. until the later parts of the 1800s. The first 99 years there were no real immigration laws here. (So roughly 40% of our history had no immigration restrictions for the most part)