Okay, so after doing some "poking around", I found the solution on my own.
In the "Cable and Harness" environment:
Step 1: On the "Cable and Harness" Ribbon, click on "Library".
Step 2: In the dialog box that appears, in the top-left area of the dialog box, select "Raw Ribbon Cable", and in the window below, select the only thing available: "Standard Gray"
Step 3: Pick the closest pre-existing ribbon cable type to the one you need to make. I selected the "28AWG_16Con" to make the subsequent 15 wire ribbon cable I needed.
Step 4: Click the "Copy" button on the top-left side of the dialog box>
Step 5: Select the copy that will appear just below the original one that was existing, and click "Edit"
Step 6: Edit the "Properties" and "Physical" fields as needed to create the new Ribbon Cable file, and then click "Save".
This should yield the correctly sized ribbon cable with the correct number of wires.
The Library Button

Edit the Properties and Physical Attributes & Save
Intel Core i7-7700K CPU @ 3.60GHz
64GB RAM
Windows 10 Professional 64-Bit, Version 22H2 - OS Build 19045.6691
Autodesk Inventor Professional 64-Bit Version 2025.4 - Build 407