TIN Creation

I’d like to be able to select multiple point grids when creating a TIN. I have a project where it took me 3 different LiDAR flights to complete. I combined the flights into one project. One area, the low-pass setting was needed while the rest used the Smart option. But, when I go to generate the TIN, you can only select one of your grid of points and can’t make a complete TIN of the project.