This is something I've been wondering for a while, where do the E-Series designations for the regular enemies in the Sonic Adventure games come from? I don't recall them ever being mentioned in the manuals or strategy guides, aside from a brief mention that Egg Keeper is an E-Series robot. http://info.sonicretro.org/E-Series_Robots
The only time it is mentioned in the actual script of the game is when Gamma gives his pre-level monologues. And he is of course referring to the specific E-100 series. "My mission is to save my fellow E-series friends! Search commencing."
I'm pretty sure it is mentioned in one of the Japanese strategy guides. Which one escapes me at the moment, but I know it is from a Japanese source. Those designations weren't just pulled out from nowhere.
I'm sure they were mentioned in the manuals and the mission modes. Examples being that the monkey is something like E-111 etc. There are definitely official documents but I'm at work, so I'll have to go home and have a look.