With Respect. I understand the challenge of budget restrains and owning a car. It is one of the reasons, in my youth, I sought an accredited college automotive service technician education. But to the matter at hand.
The parts supplier will no doubt have a disclaimer about the suitability of parts written somewhere noting also the customer's responsibilities. The owner is ultimately responsible for vehicle's compliance.
When I posted the BOSAL Link I realized that there was an interesting "Loophole" that did not exist, to my knowledge, when I had a BAR Smog License in my native California. Quality vs. Price and "Universal Cat" vs. "Direct Fit" issues aside, what these parts suppliers are saying, if I understand correctly is that, IF, a State requires cars purchased NEW
within their state to be both Federal EPA & CARB Compliant and enforces post new purchase CARB / Californian Bureau of Automotive Repair "Smog Check" requirements, then the parts in question must be CARB compliant if the car was delivered from the Manufacturer as CARB Compliant.
The question would be if, regardless of the reasons for doing so, a CARB Compliant vehicle has its CARB Compliant exhaust emission controls removed during the course of repairs and replaced with EPA approved parts that are not CARB Compliant, would the vehicle then be out of compliance if it where ever resold or registered in California, NY, or Maine? The answer seems to be yes, based on the the information provided by the suppliers you have noted and on BOSAL's website too. Yet it appears, you do not have to be CARB compliant in your State, even with a CARB compliant vehicle. Though it is inferred, smog inspection or not, that you must remain Federal EPA Compliant.
Aftermarket CARB Approved replacement catalytic converters must have a minimum warranty of 5 years / 50,000 miles. After January 1, 2009 CARB approved catalytic converters are required to not only have proper and existing EPA labeling, but will now also include a CARB Approval Number and the Manufactures' part number and production date.
For further information about Aftermarket Catalytic Converters and CARB requirements, please see the attached link: