User blog comment:Martialmaniac/Ten - Is it worth mentioning?/@comment-31525652-20180417024512

Are we really sure that all Nen users are capable of using Ten? Maybe some only know Zetsu for example? Like Gon at the Hunter Exam, though that's a very specific expection. Still, not all learners have the affinity to fully learn Ten before other basic or even adanced techniques. Correct me if I'm wrong, but didn't Tserriednich learn Gyo before he could control his aura flow from leaking, aka learn Ten?

For your first question, I would only mention it if it's stated in the manga. Other than that it's unnecassary and might be speculative in the rarest of chances.

Their Ten proficiency, whether literally stated in the manga or hinted at, should also be mentioned. Albeit in the latter case, it's better to word in a way so it's not being regarded as a fact.