There's a subtle difference in 3D Models which can have vertices as just the XYZ coordinates (such as 3DSMax) and vertices which include a normal and texture coordinates (such as the ISI games and 3DSimED).
I think Maya is counting XYZ coordinates so the 3DSimED count will be larger as a unique vertex must also have unique normal and texture coordinates and there is no unique count in the FBX unless the data is stored 'by control point'.
If there is an option in Maya to export to FBX storing the vertices 'by control point' this will reduce the number of coordinates created by 3DSimED as the number of unique coordinates will be known.
However, without the model (and Maya) it could well be that there is some other reason .
When importing FBX into 3DSimED 3.1E (and previous versions), the Total Point count of a model is sometimes 3x-5x the amount of points I have in my 3d modelling program.
It looks like there is some form of point overlap, where the points are being created several times in the same location, after purge they do reduce but not to the extent the 3d program can reduce them to.
Would it be a export setting within GMT or export setting with FBX from Maya?
First image is FBX export from 3DSimED, and import into Maya.
Second image is Maya after point merge to 0.00001 (without forced merge).
Third image is import FBX into 3DSimED.
It does reduce to around 90-95% after you save to GMT and purge but why can't it be 96470/165409 instead of 145000~/165409?
This severly alters game performance and file size.