I'm sure many of you have or had this in your Youtube suggestions, but for those of you who don't:
Sega's official 60th anniversary "Sega Test" study guide: Get to know SEGA better this winter. This is training for an online contest in January I think?
https://youtu.be/wqdN_L4YaDEI found this fascinating! It discusses the 10 years of Sega's console releases between the SG-1000 in 1988 and Sega Dreamcast in 1998, and in particular the planet codenames.
edit: The next installments which I haven't yet watched:
https://youtu.be/HRLGPRHFiQE - Sega Seminar - Consumer Software
https://youtu.be/b2bQDnD5D5E - Sega Zemi - Arcade Trading Cards
https://youtu.be/DkHyxJeM8Hk - Sega Seminar 4th Session - Virtua Study Abroad: Europe Studios