What's the difference between early and late cat delete pipes?

[jaykay]

Originally Posted by Dave80GTSi

I had ECU Doctors down in Florida do a ROW flash, which eliminated the need for the secondary O2 sensors. Then the remaining pair of primary sensors were fitted to the existing O2 bungs in my Circuit Werks secondary non-cat pipes, using the cable extensions which I've shown above.

Several years later, I've been very pleased with the results - No error codes, and a notable increase in power and rev-ability over stock.

I see, yes ROW would do it. Did you somehow remove the secondary leads such that they could be put back if needed?