Last Value is not only TerrainTypeInfo, it's limited from [0,10], not using the last [11,17] values.
I've been looking at "seed-tiny-single-072110" and the first TileData Elements are:
<TileData>91,1,0,0.000000,0,6</TileData>
<TileData>1,1,1,0.000000,0,6</TileData>
<TileData>1,2,1,160.000000,0,7</TileData>
<TileData>1,1,1,0.000000,0,6</TileData>
<TileData>77,1,0,0.000000,0,6</TileData>
<TileData>2,1,1,0.000000,0,6</TileData>
Edit:
I think i got it? Looking at the "seed-tiny-single-072110" map and using your counting method, the 3rd value at 1 is "Fallen environment" and 0 is "Baren environment"