Ascended House Rules: In the original game, the player roles are supposed to be randomly distributed, but a large number of players prefer to let people choose their roles, or otherwise create a draft system that gives players a greater degree of control over what role they end up with. A few of the spin-offs adapt this into the official ruleset; Reign of Cthulhu for example gives the first player a choice of two roles, with the unselected role being passed to the next player alongside a new one for them to choose, repeating until everybody has selected their role.
Development Gag: The second edition of the game replaces Toronto with Montreal. The Montreal-based publisher Filosofia bought out Z-Man Games in 2011, so that is a nod to them.
Comes full circle with Pandemic: Hot Zone, which has both Toronto and Montreal as locations; this is due to the fact that this version of the game focuses on North America rather than the whole world.
In addition, the announcement of Pandemic: Hot Zone was intended for the February 2020 New York Toy Fair, and its existence was leaked via printed materials made for the event, but it was pushed back out of respect for current events. The game would instead received a low-key official announcement on Z-Man Games' website in May.
The original Pandemic demonstrated that board games could be strictly co-operative and accessible yet still provide an engaging and challenging puzzle with replay value. The number of co-operative board games on the market notably rose after its release.
Later, Pandemic: Legacy would do this again for legacy style games. While it had been done before, most notably in Risk: Legacy with which it shares a designer, the introduction of a strong narrative element was extremely well received and once again caused a rise in the number of legacy games being produced.
Milestone Celebration: A deluxe version of the base game was released to celebrate its 10th anniversary.
because of the then-ongoing (and still-ongoing as of this edit) real life n-Coronavirus outbreak