Cults aren't about a rational explanations for the authority of the leaders. They're social constructs and as such they rely on social pressure to maintain the obedience of the r/f. The jw "Bible study" with potential recruits likewise isn't about providing arguments that stand up to scrutiny - it's about putting two nice looking people in a room with a potential recruit pressuring them to accept the answers given in the wt publications. All it is is a show - two people are in front of you, demonstrating that they accept the validity of what is written so you instinctively feel like you're crazy if you don't accept it. That's why people in a weakened emotional state are the ones to get recruited - they don't have enough emotional fortitude to stand up to these people and press the questions.
All this means that they can simply state that they're the fds, and it likely won't affect their recruitment, because it's not about logic and facts. If it were, cults wouldn't exist. As long as there's an answer to every question (and by that, I methe one jw will say something in response and the other jw will nod approvingly) the social pressure will take care of the rest. If something doesn't make the ones susceptible to cults will just think "it makes sense to them, so I'll just accept it for now and come back to it if it still doesn't add up" the problem is that this gives the cult time to indoctrinate you and you never come back to it.
Also, let's not pretend recruitment is stellar as it is. In the developed world, they're already getting only the dregs of society... Most of these folks aren't the type to spot logical fallacy.
That's why I say they can drop 1919 and not lose anything. It's because there isn't a single new recruit that was on the fence until the 1919 appointment is explained, but jumped in with both feet after.