Here is how we should be looking at this...
1) Physical evidence
Hair, Scat, EDna, Dna, bones, flesh, teeth, etc
2) Trace evidence
Footprints, teeth marks, audio recordings, video recordings, tree structures, slide marks, body casts, etc
3) Witness reports
sightings, observed trackways, heard unexplained sounds, etc
4) Hoaxing
trackways, video recordings, audio recording, etc
Basically we are stuck with 2, 3 and unfortunately 4? And we are trying to get to number1!
3 has little value. 2 has some value in getting us to number 1. And as of yet no one has produced number 1 in an acceptable way to science.
Number 4 plagues us because some people think it’s funny, some people thinks it will strengthen their cause and some people want to cash in. In the end? It’s number 4 that hurts us the most and why science doesn’t take the subject seriously.
There may be another category.
5) Conspiracy
Some people feel like the government is covering it up. Not unlike UFO’s.... which now seems to be the case after the Navy admitted that UFO’s are real. After debunking them for 60 years. Will at some point in the future will we see the government admit Bigfoot is real? That secretly they have been studying them all along? Is this an avenue we should pursue?
And the last category that has to be addressed is this.
6) Non existence
Either it went extinct or never existed at all. We are all wrong. The tracks I saw where caused by x,y or z. Witnesses are seeing bears while intoxicated. Etc, Etc, etc. Not a pleasant proposition to consider. And yet we seem to have serious problems getting to 1. Logically should it be this hard? If there is truly a healthy breeding population of large primates living in our forests? All species get sick, wounded, die. All species leave behind feces, blood, saliva. It cannot be helped. So we need to self examine WHY we are not succeeding. Is it because we are seeking something that isn’t truly there? Or are we incompetent? Are we focused on the smoke and not the fire? Is the government torpedoing our efforts?
Maybe Zimmer’s categories can play a role here. Disseminating different classes of information. But in biology this takes a back seat to physical evidence. Just like in a court of law? DNA trumps a contradiction by a eye witness account.