Duplication of mesh question

I installed a mesh from one developer. I subsequently wanted to replace this with another developers mesh for the same region. The first developers uninstall program does not work for some reason and I am wondering whether it is necessary for me to remove these files manually (I have the list from the install log that was generated).

Is it a problem to have duplicated mesh for a single area? In my case it is the African continent. I guess that unlike scenery where the priority can be set, the sim might not know which mesh files to use?