The later specs allowed for floating channels based on channel maps, which allowed Comcast to bypass those degraded channels.

Note: I'm not an apologist, but I worked for Comcast and for a subcontractor. Comcast treated (at least in my opinion) their customers like wallets that called and complained, but under the subcontractor I saw that since they didn't rewire 100% of all networks purchased, it was common that the older lines were causing the degradation and also reflection on other RF channels sometimes on the other side of an area even. Now if Comcast invested in their network as opposed to buying other companies and calling it investment, this might have been fixed, but that would be decades vs. having every modem that wasn't compliant to the new spec swapped.