This change was announced here:
There's been a slight change to the free packs that we award monthly to the Gold Members in EverQuest and EverQuest II. Starting with the launch of Debt of the Ratonga, free member packs will be awarded on the member's first log in that month. We've completely removed the "anniversary date" which confused a lot of players. Furthermore, the Gold Member MUST log in during a calendar month to get that month's worth of packs. Packs will no longer accumulate from month to month. Unopened packs and unredeemed Choose A Pack loot cards from previous months and prior to this change will not be touched. To get your packs moving forward, just log in each month! The Choose A Pack cards awarded in December may be redeemed for any regular LON booster pack from sets 1 – 14.