Please reread the definition of a tap conductor very carefully.#14 tap conductors cannot exist on a 20 amp branch circuit as they are not tap conductors per the code. They are protected at their ampacity. It appears to me that the part of the table that shows #14 taps on 15 and 20 amp circuits is not valid because the #14 is not a tap.
I think this is another case of the code using field language and not code language. The #14 connected to the #12 is a "tap" in the field language, but is not a "tap" in code language.
I think this is another case of you, like others... and not unlike myself, reword the meanings of requirements and definions in our own words. On occasion, there is a conflict between our words and the exact phrasing of the code... and this is one of them!!!
For one, the definition does not use the word ampacity. The qualifying criteria is "a conductor... that has overcurrent protection ahead of its point of supply that exceeds the value permitted for similar conductors that are protected as described elsewhere in 240.4." A 20A ocpd exceeds the 15A maximum ocpd value permitted for 14 AWG as specified in 240.4(D)(3).