I found something that might be a potential error and one that most certainly is. Potential because I changed the costume enchantments to be slightly more effective (mineffect = 10, maxeffect = 40 for Courage, Confidence, Wit and Charm).
For example, Slave A has 70 Base Charm and 75 Max Charm. I equipped her with an enchanted Kimono that adds 15 Charm. Total Charm= 85. I had her work as Public Entertainer.
Next day I found another Kimono with +23 Charm and decided to change. I removed the +15 and equipped the +23 but instead of her Total Charm be 93, it became 83.
After some tests, I found out that when you equip a slave with an enchanted item that increases one of (Courage, Confidence, Wit and Charm) stats and the result is above the Max, then you let the slave work with something that increases that stat, the slave's total stat will be forced to the Max, and when you remove the item, the result will be a smaller stat (Max - Bonus).
The other one is: The status enchantments on items counts towards specialization required stats.