here's my theory:
1. ammunition is meant to be fungible. any bolt is the same as any other bolt. when you recover your ammo, you recover half your bolts.
2. if you use multiple distinct types of ammunition, you recover half of each. if you fire ten bolts and twenty arrows, you get back half your bolts (five) and half your arrows (ten).
3. your bolts are either fungible or distinct, one or the other.
4. in making your bolts distinct, you don't simply have bolts now—you have red bolts, blue bolts, and yellow bolts, one of each. you fire each one.