third trip to China, do I need to bring my old passport bearing the previous 2 visas?

Yes, you need to bring your old passport bearing the 2 visas to prove that you are not the first-time applicants, then you don't need to provide the documents for first-time applicants, such as NBI, bank certificate, etc

Your previous 2 visas have to be the vsia sticker, those with stamped visas must submit additional documents for first time China visa applicants.