The way I read the rules is as follows:
1) You spend Proficiencies to acquire skill with an ENTIRE Group of Weapons from either: Blunt, Edged, Hurled, Bows, Black Powder or Siege Weapons. You can spend points to attain 2 levels of skill: Trained and Forte.
2) For any Weapon Group you spend 0 Proficiency Points in, means you are considered Untrained, thus take a -4 non-proficiency penalty to Attacks.
3) For any Weapon Group you spend 1 Proficiency Point in, means you are considered Trained, thus cancelling the non-proficiency penalty to Attacks with the chosen weapon group only.
4) For any Weapon Group you spend 2 Proficiency Points in, means you are considered to have Forte (aka Mastery or Well Trained), thus gaining a +1 bonus to Attacks with the chosen weapon group.
5) Certain exotic weapons in a Weapon Group require you to have Forte in the Weapon Group before you may use them. This does not change the fact that you gain your +1 to Attack with these weapons. It simply means that until you have become "well trained" (aka gained Forte), some weapons are still just too complicated to use effectively.
For instance, this is how I look at it. Simply being Trained (Proficient) in basic blunt weapons is not enough skill to allow you to correctly utilize exotic blunt weapons. Once you have achieved mastery (Forte) with basic blunt weapons, you have enough skill o broaden the types of weapons you understand the use of (gain access to exotic weapons).