A couple things about my experience with textures. Pardon my very technical language.
When texture is “applied” to the model, it does not color vertices/polygons with the colors - it maps the 2D picture to the model based on tex coords, so you get a very high quality looking mesh. This is what most mesh programs do and my lab likes to use in annotations.
When you transfer the texture as scalars to the mesh, then you lose the high resolution looking texture, now there is no 2D pic to “stretch” over the model, you see vertices/edges/polygons painted with the colors calculated from the original texture imaged and interpolated. I tried to go this route but my people complained about this saying that it is not the same quality as the camera software (3dMD or Canfield).
Another tricky thing - which happened to your mesh- is the stitching effect. This is the result of cleaning the mesh. Often, there are floating vertices edges etc that contributes to the mapping of the texture to the mesh. When you clean, you remove those vertices/edges and get that white region. I couldn’t find a good solution to this, so we keep using uncleaned original meshes with original textures. That gives the best visualization.