I just started Chapter 12 and I still only have 3 accessory spots for each character. . 4 accessories (1 by default and 3 through upgrades in the Chrystarium, though 3 is the max prior to beating the game). The 4th Accessory slot for each character will be in whichever primary role hasn't already unlocked an extra Accessory slot. When and how do I get the 4th? In few words, it's just a way for the game to reduce you capacity to wear anything, anytime; because you have 4 slots for accessories and some.