The major problem with the Zana narrative is her missing body. ...
I'd say there's an even more major problem underlying the problem of her as yet undiscovered body - the problem of the Zana story itself. Even the most detailed versions of the story contain gaps or ambiguities, among which the following are the most troublesome.
It's not clear when Zana was captured.
The widely recycled versions of the story either make no claims about the timeframe for her capture or attribute the capture to sometime in the 1850's. I have yet to find an original source (or reference to an original source or evidence) for the claim she was captured in the 1850's. The Wikipedia article describing Zana's story states she was captured in 1850, and attributes this claim to the 1996 English translation from Bayanov's book. However, the linked Bayanov text says nothing about when she was captured.
I can't determine whether the 1850's claim - much less the specific claim of the year 1850 - is reliable, because I can't determine when it surfaced or what its source may have been.
NOTE: Porshnev's account mentions there's also no consensus on
where Zana was captured. He mentions two versions - one in the forested mountains and the other at or near the Black Sea coast.
Zana's age is a mystery.
I've never seen any comment as to Zana's apparent age at the time of her capture. If she was captured in 1850, and bore a child unaided as late as the early 1880's, one has to presume she was captured at a relatively young age. None of the accounts give any clues to her age, save for two indirect clues:
- she was big enough to require being shackled for transport and delivery to her original 'owner'; and
- (assuming one accepts the childbirth dates specifically cited) she was old enough to bear a second or later child as of 1878.
It's not clear when Zana was transferred from one 'owner' to another.
The accounts all agree that she ended up in the possession of Edghi Genaba (sometimes cited as Edgi / Ghenaba) in T'khina. Some accounts list 2 prior owners (as you've mentioned). No account that I've found offers any clues to how long she was held by the first two owners and / or how long Genaba kept her.
It's not even clear when Zana died.
Porshnev's account (in both English translations) states Zana died in either the 1880's or 1890's. Some accounts specify a death in the year 1890. I have yet to see any explanation for the specific 1890 claim.
Porshnev's three 1964 / 1965 visits (to search for Zana's grave) all depended on local residents who were alleged to be witnesses to her funeral. If one accepts a death timeframe of 1890 or the decade of the 1890's, these witnesses were being asked to recall an event circa 65 - 75 years in the past. If one accepts the possibility her death occurred as early as the 1880's, one has to add up to another 10 years to the retrospective time horizon.
Wikipedia cites Zana's last childbirth as having occurred in 1884, and attributes this claim to the 1996 English translation of Porshnev in Bayanov's book. Once again, the alleged source makes no specific claims supporting the details in the Wikipedia article. If one accepts the 1884 date, this would represent the earliest timeframe for her death.