Steven,
I have no idea what was going on earlier. I just did a test export and the .mtl accurately depicted the materials used. Was having a run of anomalous behavior yesterday. I suspect it had something to do with M$ pushing some sort of alleged "update" to Windows 10. At one point I lost over 3 hours' of painstaking, delicate, cut-and-try work for no apparent reason. Luckily, I remembered most of the important details of the final result and so was able to recreate it in only an hour or so.
Anyhow, I have saved a link to the official .mtl file format and can frakking well hack the .mtl file if I need to do so.
Still do not know why the board here would not allow me to attach a 7,100Kb zip file for you. Oh well.