If you extend a 14/2 circuit with 14/2 and you discover there is a 20 Amp breaker feeding the circuit? what are you going to do?
That's basically what I was driving at. Here in my state, if you add to or extend an existing circuit, that is considered a new installation and the entire circuit must now be brought up to the current NEC, meaning proper wire size, OCP, AFCI and/or GFCI protection, where required, etc...
But, for existing circuits, you are required to use replacement materials that meet the current code, such as, using TR replacement receptacles for resi, GFCI protected receptacles where required, WP in-use covers where required, etc... but not required to bring the rest of the wiring up to current code.
Although, I'm not sure if you could actually replace an existing two-wire receptacle with a new two-wire TR receptacle, since I donít think any are available at this time.
I guess maybe in this situation you would need to use three-wire receptacles with no equipment-grounding conductor and GFCI protection.