There's no discrepancy in the numbers. Note that the article I linked to, quoting Dingman, is from 2010. Membership has continued to decline since then.
All of the statistics I cited are taken from the AMA's own annual reports, and I did that specifically so they can't say I'm reporting erroneous numbers. The 28% decline in membership is based on the numbers they reported. Others have tried to come up with independent estimates of membership based on tax documents and mailing permits for the magazine, and they claim the real figures are worse than what the AMA reports, but I am not even getting into that game. Even using the AMA's own stats, we see a 28% loss of membership and millions of dollars of financial losses in about six years.
How would someone else do better? Fair question. Also a very difficult one. I will honestly admit I do not have the answer. By contrast, Dingman has claimed to have all the answers and has been wrong every step of the way. He expected the AMA would be nearing a million members by now.
I believe the way the management of an organization, whether a corporation or a non-profit, gets the best results is to hire smart people, give them the tools they need to do their jobs and hold them accountable for results. Dingman's approach is different. He values loyalty above all else, and I mean loyalty to him, personally, not to the organization. (Here's an example
.) As a result, people who have suggested ideas other than his have been fired or marginalized and the remaining employees know they have to keep quiet and follow orders.
This is not the environment for innovation. The AMA faces serious challenges. Building the membership would be difficult for any leader, but I believe it is impossible with Dingman's style of leadership. At the rate the AMA is losing money, it will be bankrupt in a decade or less unless something serious is done.