User blog comment:Meruemgungiplayer/A Case Against the emitted Nen Beast./@comment-33963503-20190508205126

Actually a similar topic has already been discussed among Japanese readers in around 2014 to 2015, because a lot of people want to know the nen type(s) of abilities including Netero's. Since it is possible to hide conjured objects using In in the kurapika vs uvogin fight, people come to the consensus that hidden objects can be emission or conjuration. The fact that a certain nen construct is invisible tells us little about its nen type, not to mention in many cases we do not even know whether such construct are visible, plus an nen user can always use most categories of nen. All we could say is if it is visible for common people and being constructed by nen, it is certainly a conjuration. If it is visible but not conjured, it belongs to a manipulator nen.

But in my opinion your logic is faulty towards the end. We cannot just assume nen beast can only made out of conjuration, in fact many hints suggest otherwise. A belief is always a belief, and without evidence there is no "safer" one. It's just like how some people that are religious trying to justify their "intelligent design" theory, which is regarded as pseudo-science and not stated as part of formal science.

Going back to topic, actually the databook is not the only source that states the nen type of users, Razor has been explicitly stated as emitter at the back page of the jump release. This is official and comes from Togashi. In the early stage of the manga, Togashi inclined that nen users should focus on his own and close-by categories (although this is pretty much discarded later by characters like Morel and Pitou afterwards), judging by Hisoka's evaluation on Kastro and Biscuit's tutorial to Gon and Killua. I can argue that it is "safer to assume" Razor's ability is an emitter one. If we look at the behaviour itself, I would even say Knuckle, another confirmed emitter, seems to demonstrate the possiblity of emission nen beast, despite it is only stated as a curse in the manga.

In short, all we could say for certain, is that nen beast can be conjured, but we cannot say they cannot be emitted.