Yes that is how my teachers have taught me, with my understanding being that -ます forms imply the future, but -ている being the ongoing present tense. As such, if you're saying you know something it would have to be present.
Alternatively, it could just be a convention of Japanese, I'm only N4 level so no expert.
I am also not expert, but in my experience, in Japanese the verbs that are conjugated in the progressive tense -ている mark the current state of something. For example, if we talk about a TV that is not working anymore, we would say テレビは壊れていますrather than テレビは壊れました (壊れる = to break). This is definitely not the case in, for example, English and Spanish, where the participle is used to mark the current state of the subject (we don't say "The TV is breaking", but rather "The TV is broken"). Then, it makes sense if you think of the meaning of 知る as "to get to know" rather than "to know", the action of the verb 知る being a short, non durable action (to get to know, the very instant where you gain the knowledge of sth). If 知る translates as "to get to know", then 知ってる translates as "to know" (i. e. I previously got to know sth and thus I reached the state of having that knowledge about sth. Note that it is not describing a non durable action but a state that occurs during a certain span of time).
In the case of 知る, what's happening is that it actually indicates the change from not knowing to knowing, an instantaneous change in state. So, as with all verbs that represent a change in state, the ている form is used to mean "the state changed and that change persists in the present." Which is what we mean by "know" in English. The plain 知る is more like "come to know" or "find out" in English.
知ります or 知っています?
I was told 知ります is not used, only 知っています. Is this accurate? What is the difference between the two?