I too use spreadsheets a ton to plan out fictional leagues. This may be hard to read, but its a screenshot of my planned out league based on the early history of the NBA from 1946-1980. I moved everything back two decades and have been slowly making my way through the years. The left column is just notes on the logo sets I use for each team that is based on the real NBA team that existed. And then there are some other notes, the planned ABA rivalry for a few years, and then adding minors along the way.
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Native Georgian. Adopted Texan.
Las Vegas Knights GM, 3 Time TBC Champion