This is all a guess.

• 5.0 - Actual 5e
• 5.1 and 5.2 - ??? (Maybe some version of the "light" 5e rules)
• 5.3 - "5e Advanced": decoupled paths from class, increased prof, etc. Used in early 2017
• 5.4 - System 7.9 in disguise. Split into its own repo