I have two identical ADC gold-body XLM-III carts from the late 70s. I purch'd them used, as part of two turntables that were each purchased from different parts of the US. Each cart has a different model of stylus (XLM-III and QLN-2) , and styluses can be interchanged. 

The MI series from ADC should output 5.5mV, which I have not measured. However, BOTH these carts are challenged wrt output volume. Not only do I have to crank up the vol. more than 1/3 above other carts, but  the sonics are a bit "small" and not "full bodied". It might be due to weakening permanent magnetism -- these are both getting close to 50 yrs old .

The perm. magnet in ADC moving iron series is mounted in the removable stylus, just above the stylus/cantilever assemble. 

Not sure what else the low volume may be due to??? These are my my only MI carts in my collection. Anyone know more?