That's up to each individual to decide, imo.
As logic would have it, if someone suspects something to exist that they haven't yet observed with one or more of the five senses, they go searching for it. Once it's found, they wait a while, replicate the observation to see if they can observe it with the same senses again. If that's successful, it gets labeled with a name/identifier, properly classified, and then usually some kind of instructions on how to observe/understand it so that others may observe it.
If what is suspected to exist can't be observed with one or more of the five senses and passed on so others can observe it in the same manner, then it's a complete waste of time to go around saying that it does exist, imo.
We may not have observed everything there is to observe in the universe that may impact the way something that has been observed yet, but until those "missing links" are found, I prefer to classify them simply as "unknowns" and not write about them in a book as stories I make up to explain them. //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif