There may be one line to follow.
Find a witness.
You may be able to find a player that you can demonstrate was referred by you (the affiliate), and who is prepared to help with stats from THEIR end.
The more players prepared to help, the better. Affiliates who have offered help to their players, and formed some kind of "community" on their portals are more likely to get players to help - after all, the player has lost nothing, and has nothing to gain.
If the GP audit says you are owed nothing, or a very minor amount, yet players you referred are STILL depositing and playing, you can cross reference THEIR stats with what the audit claims you are owed. So long as the player can show you the net loss between Dec 2008 and the end of 2009, you can do this. It's easy for the player - pull up Cashcheck, it holds 2 years worth, and do a search from then till now. Take the figure for total deposits, and subtract the figure for total withdrawals. If this is positive, the player MAY have generated payments. If so, ask the player to do this by calendar months, this will provide data for an accurate calculation of what that player produced in revenue for the casino, and multiplying this by the affiliate commission percentage should give a figure for the commission owed from that player.
Affiliates who have been told nothing is owing only need to find ONE player whose records disprove this, to prove the audit was flawed, and produced the wrong figures.
It seems GP knew what they were doing when they asked eCogra to do the audit. By commissioning it themselves, they gained legal control over the procedure. Had eCogra themselves initiated the audit, THEY would have had full control, and could have demanded whatever information they deemed necessary, and GP would have had to comply.
GP probably thought this process would kill the issue that had been smoldering away all year, and that they would only have had to pay a limited amount out. Unfortunately, it didn't work, and they are now in an even worse situation than before, having inflamed the issue yet again.
The fact that GP no longer want to cooperate with an investigation into the fairness of the outcome only serves to convince affiliates that this was a contrived exercise from the outset, and was NOT designed to find out how much was really earned from legacy players, but to provide a means of "buying off" those affiliates who felt they had an outstanding grievance in the hope that the issue, and the blacklistings, would become a thing of the past.
With no current affiliate scheme, GP have no need to placate affiliates any more than is necessary to have the blacklistings removed.
I also don't buy the findings from the audit that for some affiliates at least, every single player they had decided in unison to stop playing, and coincidentally on the same date that the program closed. For one, it took time for the issue to grow to the extent that affiliates were blackisting GP, and players who quit because of this would have done so gradually, as first they saw the blacklisting, and then considered whether such an issue was really THEIR concern, because they may have been getting excellent service from GP as a player at the time.