Kuz 3 musketeers are chocolatey goodness & the 4 musketeers are the dudes who band together and "bring the ruckus" against taxation,the queen, & evil doers. Not to be confused with the" mouse-keteers" who sing & prance.
The 3 musketeers described Athos, Artemis, and Porthos. They are the only 3 musketeers or so it seems that do not disband upon the cardinals command as musketeers protect the king. Since the other musketees attended the disbanding; it seemed as though they were out of service. D'artagnon wanted to be a musketeer, but since he did not officially hold the title, he is not considered one. The musketeers were an elite group, sort if like the u.s. marines. The story actually focuses on d'artagnon, his desire to be a musketeer and his journey to save the king that results in him becoming one.