Yeah, if they are olympic or oval stadiums the sidetracks need to have a vertex color assigned or be appended from another model. I've never seen double goalposts, but they have weird textures. The crowds usually work well when converted with FCC. In any case, I think they are totally usable.
Anyway... here's the last existing model (as far as I know) of a FIFA NT that needed to be converted to FIFA16,
Swaziland (or Eswatini):
http://www.mediafire.com/file/lpupjvg5pcqcq8m/Swazilandia.zip/file
Next:
Tibet. It is actually a stadium in Dharamsala, India, where the Dalai Lama is living on exile, therefore it would make sense for the Tibet NT to play there, since they wouldn't be allowed to play in Lhasa or anywhere in the Autonomous Region under the current political situation. Besides, I dont think there is a model of any Chinese stadium in or near Tibet...
I hope some of my friends from PES6 would take the challenge and build at least some of the 15 remaining FIFA NT stadiums, couple from north-east Africa missing, Somalia would be great, also some more caribbean islands would be awesome.