In the TechnicalWhitepaper.md it says "The selected producers are scheduled in an order agreed upon by 15 or more producers."
While https://developers.eos.io/welcome/latest/protocol/consensus_protocol Chapter 4.2 says it is in alphabetical order.
From what i saw, the alphabetical order is true.
Or is it just default in the EOSIO Chain that everyone agrees upon alphabetical order? Then the first statement would not be wrong at least.