I personally believe the 5xx series should be considered two separate generations - Model C/505-515 (as Gen 1) 516-D80 (as Gen 2), considering the motor shell is significantly different between the 505-515 and 516-D80, as the 505-515's motor shell doubles as the outer shell, while the 515-D80 has the same basic motor shell architecture—inner and outer shell.
Which would make the Classic 1CR - Legend II Gen 3 cleaners, and the G3-Avalir Platinum Gen 4 cleaners.
Which would make the Classic 1CR - Legend II Gen 3 cleaners, and the G3-Avalir Platinum Gen 4 cleaners.