Episode #4.4 - S4-E4
Other mistake: On the first day of investigations, Florence says that "two days ago" the victim withdrew a large sum of money. A CCTV shot is shown later in the episode, establishing that day as March 9th 2015 - remarkably consistent with the date of the previous episode and the coroner's report. So it is the 11th, and the investigation concludes on the 12th, a Thursday. However, at the end of the episode, Dwayne says that it's Saturday.
Answer: There's probably no particular reason. Sets and props on long-running TV shows often change as needed and for various reasons throughout a series run.
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