semi-related, but also helps me to believe that this is the case (and not only because the different regional servers were called "shards" in Ultima Online):

in the "Game Coding Complete, Fourth Edition" book by two programmers who worked on Ultima and Sims (and other Origin/EA games of the time) back in the day, they share some war stories of programming, and if memory serves there is a portion where they talk about the original design, and the realization that lead to the sharding and how the login and shard system worked in the game.

Also, unrelated, a really neat war story about a guy who put in debug code to generate certain audio cues while a game was running to catch a bug.

The book all in all was a fun read if only for all these stories, and generally remember good coding guidelines as well but it is using older C++ that may not stand up to modern critique.

[0]: https://www.amazon.com/dp/1133776574

While I agree this is a wonderful resources, it is much less about game development than it is about design patterns. Basically, it's a gamedev flavored book about design patterns. A much better books about game development would be Game Coding Complete [0].

[0] https://www.amazon.com/Game-Coding-Complete-Fourth-McShaffry...