I never used the Ektacolor interneg films although I have printed some but I used cases of the 4114 and lesser quantities of the 4112 and its 35mm version. We started with the density difference system and wound up with a computer program that made the balance more accurate. The more accurate balance made matching PMS colors much easier. The 4112 we used mainly for copies from reflection art. We also used some of the ID variant which had an extra kick to keep the white paper white.
We also used tungsten balance neg film for picky work from transparencies that had both a contrast and a highlight mask.(mask in this reference means a low density b&w neg registered with the transparency)
After Duratrans and Duraclear came out we only used Vericolor print film for color correction masks or 35mm slides.
I have used the Ektacolor internegative film, albeit very briefly, in 1977, when Vericolor internegative had not yet made it to market. I was a student at Ryerson Polytechnic University (then known as Ryerson Polytechnic Institute), and it was part of our Third year program to produce a correctly balanced Ektacolour internegative. It was one of the few times I actually made internegs on that film, and my results were only so-so. I had problems with, AFAIR, a red-cyan crosscurve, and the colour saturation and contrast were high. This, I found out later, hinted at an imbalance in the magenta and yellow filtration, and my exposure was too great. We balanced the film using the curve plotting method, although I included a special Kodak three-point gray scale, designated Q6C, which was supposed to be a shortcut method for assessing the interneg.
We used a Meteoriette processor, for a modified C-22 process, which also included special Internegative control strips, designed especially for the modified process C-22. I remember my lab instructor, a photographer with many years experience in the industry, telling the class that he had worked in operations where the C-22 processing line had three different developer tanks: one for regular C-22, one modified for Internegative film, and a third modified for Ektacolor Print Film, which was a method of making large format transparancies directly from negatives.
We used to make a sort-of "quick and dirty" interneg using Vericolor Professional film, Type S (VPS). The procedure was to enlarge a transparency onto it, and then to flash the film before development. The exposure was something like 1 second @ f/16, for 35mm to 4x5, using a Chromega enlarger, equipped with a colorhead. We would dial in filtration to simulate a Wratten 80A filter, about 100 cyan plus 60 magenta, or you could use an actual filter. After all of your transparencies were exposed, you would flash them through a 2.0 ND filter, plus (I think) a CC20G filter, using the same exposure and filtration used for the image making. The prints which resulted from this procedure were okay, but they weren't as good as prints made using Ektacolor Internegative film.
So it was no surprise that when the Vericolor inteneg films were available about 1978, their arrival was greeted with cries of joy (and I'm not kidding about that; I distinctly remember one of my fellow students holding a 50-sheet box of this film in his hand, and wildly gesticulating with both arms, and saying that he could now make Type C prints from his FAVOURITE 'chromes!). They required unmodified C-41 processing, which was a blessing. AFAIR, there were two types, 4112, for internegs from other than Kodachrome originals and for flat copy work, and 4114, which was for internegs from Kodachromes. We balanced the film using the curve plotting method.
When I entered the full-time workforce, after graduation in 1979, I made rather a lot of internegatives (rather...) on those two films. I also used the 35mm vesion, in modified duplicating equipment, to make internegs from 35mm slides, especially for Christmas Card production. The one thing I never did do was to use it for copy work, as it was just too slow, and it was not a viable option to expose it using electronic flash; I had a chance when on a training course at Eastman Kodak's Marketing Education Center in 1987 to speak to one of the company's experts, and I was warned off that idea.
In the 1990's, a new internegative film was available from Kodak, Commercial Internegative, and worked quite well. I used to balance that using the density difference method, based on contact exposures of a 21-step silver step tablet, with feedback provided from the printers, on the balance. I used to change the red-cyan balance for Kodachromes, as we experienced a crosscurve when they were given the same exposure and filtration as Ektachrome originals.
Fuji also marketed a nice internegative film, too; I had a chance to "test drive" it, about 1993. Management of the lab in which I worked decided to stick with the Kodak product.
Any of the dedicated internegative products I used over the years, when properly filtered, exposed and developed, would make beautiful prints. Sometimes, filtration and exposure would have to be modified, to suit a particular need. I remember making internegs from slightly faded, blue transparencies; the interneg filter pack required a change in the yellow filtration, and slightly more exposure. The final prints were better than the originals! And I made many, many internegs from underexposed transparancies.