I can now confirm (most) of your results. You do seem to have a slight issue with that one entry that didn't decrease.
Here is what I found in a table in the exe.
Vehicle Limits
---------------
# Players, # Vehicles per player
1, 200
2, 160
3, 115
4, 90
5, 77
6, 65
Building Limits
----------------
# Players, # Buildings per player
1, 250
2, 175
3, 100
4, 75
5, 50
6, 48
Mind you, this is when the build buttons dissappear. If you've already built the structure kits, or told the vehicles factories to produce a unit, but they haven't finished yet (or been deployed yet?), then the button still won't be disabled. So there is a small window of opportunity to build past those limits.
Btw, we might potentially have enough info now to change those limits.
And just think, Friday is right around the corner. B)