I was trying to answer the question as a student might answer the question. Since there are three chirality centers, therefore there out to be eight possible compounds. This is similar to a compound with two chirality centers and if symmetrical, then a meso compound exists for two of the apparent isomers. They turn out to be the same compound.
I had looked at it from the way that symmetry reduces the number of compounds by formation of meso-structures. In that, two of the compounds also degenerate into a single compound, as you have noted or by a flip as I have noted. However, as you point out, these compounds are not the enantiomers of each other, which are listed side by side. The enantiomers are chiral and therefore not meso.