Information linking emails to Bitcoin addresses has been provided. The next step is to contact the email address and request a signed message from the respective Bitcoin address. Once that is done, it's reasonable to conclude the owner is legitimate.
Let's sum things up here:
I. GIGAMINING shares were being traded on the GLBSE platform.
II. GLBSE is discontinued (in the most disorderly way possible).
A month passes.
III. The operator is tagged as a scammer.
Another month passes.
IV. A list of asset holders is produced, by the ex-operator now tagged as a scammer. This list is declared incomplete by the author himself. The list is delivered as plaintext over mail to the issuer of GIGAMINING.
This brings us about up to date. Of the multitude of people on this Forum (F), some are (Fo) and some are not (Fno) owners of GIGAMINING shares. Those who claim shares (Fc) will be some but not all of Fo and some but not all of Fno. Of the Fo, some but not all will be on the list. Of the people on the list, it is at this point hoped
that all are in fact Fo.
There's a lot of sets, a lot of overlap and pretty much nothing definite to go on. Anyone can claim they're in the Fo. With the information so far available there's not in fact any way to either prove or falsify such a claim. Being able to verify the control of a Bitcoin address is a good step forward. However, NOT being able to do so does not necessarily prove anything. Suppose the person used an old wallet they meanwhile abandoned to send money to GLBSE a significant interval ago and never since made withdrawals. Suppose the person only used a 3rd party, such as for instance some webwallet service that doesn't support signing or that mixes client funds.
So look at it from the other end:
1. Person makes claim for Fo, is on list, is able to sign with address. Are they a legitimate owner? Maybe (unless, for instance, they colluded with Nefario to falsify the list for their benefit - which'd be one possible explanation for the delay).
2. Person makes claim for Fo, is on the list, is not able to sign with address. Are they a legitimate owner? Maybe.
3. Person makes claim for Fo, is not on the list. Are they a legitimate owner? Maybe (and they for any of a host of reasons weren't included).
4. Person makes no claim for Fo. Are they a legitimate owner? Maybe.
All I see is Maybes. For this to be resolvable painlessly i'd have to see nothing but Yes or No. No Maybes.
Now, you say "it's reasonable to conclude". Is this you offering an indemnity, in the sense you'll pay out of pocket anything and everything if that assumption turns sour? Yes, my choice of words may not be to your liking. Sticks and stones.
Sticks and stones, because this is a story of sticks and stones, and apparently words cannot quite paper over the chasm of a categorical difference.