The simple answer is there were no real standards to go off of and the communication that we have now withe forums and the SCTE has exploded in the past 25-years. I remeber at Adelphia when we had Lan City modems and we new nothing about noise mitigation and the reverse balancing was a camera aimed at an analyzer with a modulated channel you watched on a TV in the field.
This is CABL.com posting #371845. Tiny Link: cabl.co/mbITF