Well, it looks accurate through October 2003, but I'm guessing that inaccuracies in the ordering prior to that are probably due more to our own setup rather than Simple Machines (SMF).
Yes, whoever wrote that routine sorted it based on members' ID numbers rather than the date they registered. In their defense, the two would correspond perfectly if we'd been using YaBB SE from the start rather than beginning with YaBB SP. However, when we converted from SP to SE, member info was written into the database alphabetically, based on usernames rather than date registered, so A.I.Collins has ID #1, AAvolon has #2, ABarnabas has #3, etc. That's why almost everyone who registered prior to October 2003 comes up alphabetically rather than chronologically. But when I get a chance I can easily fix the script to sort on date registered rather than member ID number.