Trivia / Ace Attorney Investigations: Miles Edgeworth
Development Gag: Edgeworth reconnects with Penny Nichols, a minor witness from the first Ace Attorney game, in "The Grand Turnabout". Edgeworth notes internally that while he spoke with her numerous times, he had completely forgotten who she was until she introduced herself again. This is a reference to the fact that even the development team found Penny so utterly forgettable that simply remembering her name was considered a mark of accomplishment.
For the game itself: Ace Attorney Investigations, before that title was bestowed, was called Perfect Prosecutor by the fandom (though early announcements in Nintendo Power magazine also used that name).
Serendipity Writes the Plot: Edgeworth's flashback to the DL-6 incident in the 4th case is masked heavily and bordered by a "cloudy" filter (in addition to the series standard of merely putting flashbacks in black and white) to hide the fact that it is reused from the original GBA game (and thus has a 240 × 160 resolution with a 15 bit color depth on a 256 x 192 screen with 18 bit color depth) while Investigations is otherwise free of such sprite reuse (contrast Apollo Justice, where such reuse is very blatant when it occurs).
This also explains why Gumshoe looks exactly the same except for his tan coat. Gumshoe was dressed that way in Trials & Tribulations during case 4, which takes place in the same relative era. Back then it was due to the inability to fit an entirely new sprite in the game for a character who already exists so they just did it via Palette Swap. The DS has considerably more storage space for sprites but Gumshoe still retains the same physical appearance because that's what he looked like as told by the third game.
Concept art for Shi-Long Lang featured him shirtless, with the constellation of Orion scarred on his chest. Seems the director objected to the toplessness, even after a feather boa was added to cover the nipples.
A trailer shows Kay appearing in Turnabout Airline. Whether this means Kay would have first appeared earlier, or that Turnabout Airlines was originally a later case, is anybody's guess.
Originally the concept of the game involved Ema Skye as the protagonist and the game would focus on forensics tactics.
Concept art sketches show that Quercus Alba's design went through a phase with him looking much more like a gnarly old tree.
Before it was a Detective simulator, it apparently was going to be a dating sim.