Interesting, well; it is possible, that the ecm had the code that was persistent or remained (in memory); just like mine but that driving the car... caused the code to go away after awhile (because the readiness code was finally generated).
Ross-Tech: VCDS Tour: Readiness
With VCDS; you can generate readiness codes with the software but the ecm with generate these as you drive the car in different conditions and then "pass" the onboard emissions test of the system.
I would be interested; in knowing what part numbers specifically, that you replaced the original parts with. Its good the CEL is gone and things seems to be working ok.
If you had VCDS; you could read live data to "see" what the readings of the 02 sensors are/were; to determine if they are working as they should.
Your new 02 sensors; maybe fine but I always want to double check and confirm that you have the right parts for your particular year, engine, spec, etc.
If you are able to find your receipt or other info about the parts you installed; please post that info up. Do you mean you got the parts from "Rock Auto" online or somewhere else (I am not familiar with "Rockway auto" ? If it is RockAuto online; you can login to your account and the parts you ordered; will still be shown/saved in your online account. You are referencing driving so many "kilometers"; are you in Canada?