The -K designation for a Communications module comes from as far back as the 1771-KA, which was a Data Highway (1, not Plus) communications module for the PLC-2 front port link.
The closest functional equivalent to a DF1 to Network module is the 1770-KF2 (DF1 to DH+) box, so the SLC-500 platform DF1 to ControlNet interface got the moniker 1747-KFC, with the "15" added to distinguish ControlNet standard 1.5.
I sold and supported only a small handful of SLC-500 systems with ControlNet, but one of them still runs the busiest bascule drawbridge in the world, just a few blocks from my house.