Creator Breakdown: Unlike other shows in the franchise, which are ensemble affairs, CI focused nearly-exclusively on Goren, and required Vincent D'Onofrio to have a punishing workload. D'Onofrio eventually had to be hospitalized for clinical exhaustion, so the producers brought in a second detective team and began the alternating format in consideration of their lead actor's health problems. Goren's weight gain throughout the later seasons of the show is also attributable to D'Onofrio's health issues.
Old Shame: Chris Noth considers his time on the show to be this, not because of the show itself, but rather his poor working relationship with Dick Wolf. The men have had bad blood since the controversial removal of actors Dann Florek and Richard Brooks, as well as the firing of Michael Moriarty from Law & Order back in the 90s. Eventually, this led to his own firing from said show after he openly complained about Wolf, which resulted in his character written off as being transferredto Long Island for ten years.
Real Life Writes the Plot: When Kathryn Erbe became pregnant with her second child, a pregnancy arc was written out for Eames in which she acted as the surrogate mother for her sister's child. This of course resulted in an Obvious Pregnancy later that season.
Also the case with Julianne Nicholson; her first pregnancy was avoided by having the character Put on a Bus for the first half of Season Seven, but the second time they wrote it in.
When Jamey Sheridan was affected with Bell's Palsy, so was Deakins (who donned an Eyepatch of Power). At times it was obvious the poor guy was visibly struggling with it and was having a hard time saying his lines.
Imagine if Goldblum had decided to film a few more episodes for the series ender. Nichols and Goren cracking a case together would've just been awesome.
Apparently, there were plans to write an episode that revealed that Nicole Wallace wasn't dead, but said plans never came around to making it into an actual episode.
There were plans for L&O, SVU, and CI to have a major crossover with Goren being the central character investigating a potential terrorist plot. Then 9/11 happened and the plans were abandoned and never revisited while the Mothership and CI were still on the air.