They might simply have been lost in the crowd or not even noticed, depending on where they were posted. How carefully have we studied the variants in animals?
As for variants in animals, that's a possibility. But it's more likely to be a red herring. Domestic animals will be infected with the same strain as their owners, and any reinfection would be very likely to be similar to the original. Transfer to a wild animal reservoir and back into the human population is so rare and unlikely that it is barely credible. Infection of humans from wild animal reservoirs is a rare event. To have it happen both ways within 12 months is not credible.
I could be wrong. This will only be answered by collecting more data to improve our understanding.
We could easily miss whole strains of the virus but because non of them lead to a new dominant variant we never know the even existed.
The starting point for the omicron cluster would be an interesting bit of information, but it doesn't necessarily have any bearing on where the intermediate strains are located. But none of that matters. If it's out there, it will eventually be picked up by PCR. We can use phylogenetic analysis to retrospectively reconstruct the evolutionary tree of every organism we have sequenced to date. Doing it just for the coronavirus variants is not hard (I have done it in the past including bootstrapping). Whether it's a month, a year or a decade from now, we will be able to answer the question by reconstructing the tree.
This is really basic bioinformatic analysis, in routine use for over two decades. None of this stuff is remotely new or groundbreaking.
The other questions you are asking are not really relevant to the problem. The virus does not survive long outside a host; it has no bearing upon the problem at all. The same applies to inside the host. All variants will continue to infect and propagate themselves to varying degrees within the host populations. It's endemic at this point.
One other point to bear in mind is that the mutation rate of the polymerase is effectively a constant, in terms of mutations per n kilobases. So we would expect all variants to accumulate a certain number of mutations averaged over time--the sequence will not remain static since the virus has to continually be passaged through mammalian epithelial cells to maintain and propagate itself. There will be some variation, but if it's been frozen down and manually propagated, it may have a dramatically different number of mutations compared with the other contemporary strains that have spent most of their time in living hosts.
