So I had the p420 code come up, changed my o2 sensor in bank 1 which the code stated had the inefficiency. 50 miles later after a code reset the code is back. Does this lead to believe that the actual catalytic converter is shot which the car dealer thought it might be?

I plan on doing a flexible up pipe soon, would this replace the front cat that might be messed up or is it a whole different section? thanks guys