Trallee,
Minimum actual tooth thickness is the value of the max effective tooth thickness minus the manufacturing variations fo lead, profile, adn spacing (gamma) minus the machining tolerances. Tmin=Tvmax-(gamma+m).
Maximum effective tooth thickness (Tvmax)has three different formulas all for different spline angles.
30 deg=(pi/2P)-es
37.5 deg= ((.5pi+.1)/P)-es
45 deg= ((.5pi+.2)/P)-es
I hope this helps.