Study "Preach My Gospel" diligently and carefully. It really is amazing - so different than what I had when I served that it's like a doctoral dissertation versus a kindergarten primer. I'm not sure everyone is aware of how radically the training of missionaries and teaching of investigators has changed in the last decade.
The missionaries are not sent out to teach church history or former teachings or anything but the principles of the Gospel as outlined in the materials they are given. The simple fact is that many members (baptized, confirmed and endowed members) struggle with exactly how to understand and present certain aspects of our history and theology - and to separate what is legitimate from the incorrect traditions of our fathers. To expect missionaries to be able to deviate from the core principles and basic narrative - to actually discuss and "teach" and correct those types of concerns - is unrealistic and unfair (to both the missionary and the investigator). Those conversations are important to those for whom they are important, but they should be addressed with a regular member - not the missionaries - leading the discussion. (That also helps the missionaries learn, and I have never had a missionary object to that request.)
Finally, no matter what kind of statistical measures and pressures are used (which is contrary to the instructions of the book itself) or the personality of the Mission President and leaders, the key is to stay focused on the people and the message. Not everyone will have the same numerical results, even if their levels of faith and dedication are identical - and that is emphasized in "Preach My Gospel" multiple times. Do your best; stay focused on your actual "mission"; love the people with whom you serve and associate; don't compare your own efforts to anyone else's - and know "Preach My Gospel" backward and forward.