Windwalker, you speak of “the PGC’ as though they made some official announcement as an agency.
I remember in about 1955 -1957 period, a barber, (Richard Daveler), from our town of Marietta shot a canine while deer hunting in Potter County. It was thought to be a “wolf.” It was later checked out by the local “Game Warden,” (Russell Shope), who saidsomething to the effect of he doubted it was a wolf but looked like an exceptionally large coyote.
It was not too many years after that another canine was shot along the river in York County and it was said, (by PGC),to be a coyote.
That was about 50 years ago and it was all the talk of the area at the time.
Yes, there was speculation as to coyotes breeding with dogs but that seemed to me to be a local myth that was not anything the PGC officially claimed. If you can show me evidence to the contrary I’ll gladly accept it.
The incidences were so rare at the time that nobody really knew what was what.
Irecall it was the PGC flat out stating (in PGN), that our coyotes were not “coy dogs.” I can’t tell you what year that was but it was a very long time ago. (decades)
We need to keep in mind that back then the technology simply didn’t exist. Even something like communication between regions was reliant on telephones – no call waiting, no answer machines, no voice mail or call forwarding. When the PGC finally had some evidence and genetic testing available, they were quick to clarify the wolf/coyote hybrids. That also was “decades” ago.
As for wild dogs, they definitely were a problem in some years and many claimed them to be coyotes when in fact they were not. In my area here, in the mid to late 70’s there was talk of “packs” of coyotes numbering 10 and 12 at a time, killing sheep and chickens.
Myself and many others believed it. At the time I didn’t know that our coyotes do not travel and hunt in packs. They hunt in family groups much smaller than the packs of the western coyotes.
One day as two friends and I were building my first cabin I had to go to town for some materials. I left my two friends and as I went out the dirt road a neighbor stopped me to tell me coyotes had attacked his sheep during the night and to keep my eye out for them.
When I got back from town, both my friends were perched on the roof trusses. They told me 9 wild dogs came through and had them “treed.” The next day I killed two of them and that same neighbor killed two about a mile away. I think all were killed in the following weeks as they kept returning to attack the sheep.
So much for the pack of coyotes. (even though we "did" have some coyotes here at the time)
You cannot blame anyone for not knowing the true extent of coyotes in the early years. PGC stated that coyotes were known to exist in the N.E. since the 1920’s, but they did not have the means to verify or estimate how many and in what range they were.
A lot of these post imply “cover up” or conspiracy” and it simply ain’t so.

As for mountain lions, read back. No one says it is impossible that some exist. To date, each and every ML that has been verified has been proven to be pets.
Now, if you want to believe there are “wild” populations, that’s up to you. But the rest of us are saying we need more than “someone said” evidence.
You say “it” has been proven. I ask, “what” has been proven?
“Proof” of wild Ml's is not someone saying they saw them.
And, as you point out, in many cases "seeing" them isn't even proof is was a pet ML.