No it's just... It's kinda stupid, no offense to people who have it like me, but I have a rather mild case of OCD. So, seeing four of every kind of monster girl except for the cowgirl is just slightly off-putting, since I didn't know you could only capture three cowgirls.
Originally I only had two of each type of monster girl so that I could complete the anti-magic, anti-heat and anti-cold armor quests for my army. However, once I found out I needed more than two of each type for Mia's vanguard squad I went out and captured four of each type.