OMG can people read this very very long thread before posting stuff that has already been covered many times. It clearly states that this ban was for the next Scottish League Cup game, if it was transferable (which I don't believe it was) it was never served, so that point isn't valid.
It will be interesting to hear the formal response the club receive. I don't think it will change the outcome, but I do think someone has to hold their hands up and admit a mistake somewhere along the line. Hearts and Danny Wilson would both have known about the outstanding suspension but checked with the SFA and IMHO were given wrong information. The information did not have to show on his transfer paperwork as it was over a season old and was not applicable to his time in England. You have to check the disciplinary records to look for suspensions and my guess is that this is the bit where an admin error occurred. Ultimately the responsibility lies with the club to ensure no suspensions and Hearts can defend themselves because they asked the SFA for clarification and were told he could play.
That's a brief summary through my eyes. I don't have the time or inclination to spend the hours that many have done doing the research on this but the above is kind of the highlights from those posts