There are plenty of sea level gauges around the United States, some having been in operation over 100 years. NOAA has analyzed these quite a bit and they show some sea rise over the years. I estimated an 8 inch rise at Key West over 100 years based on their data.

I believe the point of all these studies is not to look at what happened, but what will happen well in to the future. The past 100 years is not a good way to estimate future changes in the ocean. That's not a good retort, but the biggest changes have not happened yet. A 6" rise in the last 100 years is still not insignificant.