Two additional days of filming were necessary because David Livingston had directed the episode so tightly that it came in about 9 minutes too short. Additional scenes were written, and showrunner Jeri Taylor was so impressed with the quality of the extra scenes that she defied anyone to try and identify the 'filler material'.
There was a slight error when it came to encoding the sound effects when this episode was made in post-production. This resulted in some of the sound effects, namely the sound of the proton bursts, doors opening and closing as well as others, sound off, they sound tinny and monotone. As this happened on the master copy of the episode it is seen in all the subsequent versions of it including the DVD version and streaming versions on Netflix and other sites. This issue would need to be resolved by remastering the original master copy of the episode but as of March 2020 CBS has no plans to remaster Star Trek: Voyager (1995) or Star Trek: Deep Space Nine (1993).
47 reference: Torres says she has tried remodulating the comm frequency carrier five times - on 47 different frequencies.
47 reference: Kim reports there are '347 and counting' Vidiians on board Voyager.
4077 reference: The quantum analysis of the duplicated Voyager has the heading 'Scan Analysis 4077'.' 4077 was the unit number on M*A*S*H (1972) and the number 47, in different variations, i.e. , '4.7, 0.47, 4077, ' etc.) were also frequently referenced on displays, padds, and computer readouts in Star Trek: The Next Generation (1987)), and the other Star Trek spin-offs.