Curt and I, being the Atari historians/researchers that we are, had access to the original developers in some cases, original source code, design notes, the actual games, etc. In the case of Breakout for instance I worked several years ago with Al Alcorn on getting a logic based PONG simulation engine going, which the Breakout engine uses. We also play tested it directly with an actual Breakout machine as well. I also wanted some authenticity, so I took the time to simulate the color overlays as well. The sounds are direct samples from a Breakout pcb. I went through several versions of this, with one of the original ones having the full control panel complete with spinning knob reproduced.
Unfortunately we could only go so far with what we wanted vs. what Taco Bell/Atari wanted. I.E. they wanted skill levels, and the tradeoff was no extra lives for instance. We wanted more cabinet simulation and they wanted nothing but the bezel and even that had to be trimmed down. They gave me an insane design schedule (one game a week), so there wasn't time to say...add the full scrolling landscape that you can do at a distance in Lunar Lander, or work through to get every single color change cycled accurately in to Centipede, etc.
Same with the evolved versions, where they insisted we use the graphical and sound assets from the already done Stainless evolved versions (PSP, etc.). We forced a compromise and cut out all the ridiculous Jeff Minter wanna-be colored light fests that were in the original Evolved versions. Some specific instances of negotiations I remember - 1) I took the time to design an updated ship that was actually a cross between the one shown in the coin-op artwork and 2600 box artwork, since that would bring it closer to the original vision. They said no and that it was to confusing to tell which was the front vs. back (even though the front has the blasters and the back has the thrust flames). So we took the graphic and dumbed it down to the pie slice shape. 2) They wanted us to start spinning the asteroids and such. We said no, then it would be Asteroids Deluxe Evolved.
3) They thought the saucer mad it to hard, so they had me completely pull it out of the intermediate and beginner versions and dumb it down more in the arcade. I came up with compromise of keep the arcade normal, varying the appearance frequency and in the others.