Looking at the Rio Grande Wikipedia Again

So I was looking at the Wikipedia article that I edited, and was disappointed that my changes did not stay. When I went to look at the page the changes that I made were not set. I had edited the demographic data that was on the page to be more accurate. The data provide was not the data for the Rio Grande Valley but rather the data for just the city of Brownsville. So I edited the page to represent the entire Valley. However upon further inspection I just noticed that the demographics part is not actually part of that page. When I tried to edit the section again it redirected me to the Brownsville page and would not let me edit this section for the Rio Grande Valley. I am not sure how this happened I will continue to try and edit the page to make it more accurate so that people can learn about the whole Valley and not just Brownsville.