I am assuming for this design the triodes in the 6sn7 that are not electrically equivalent don’t create a problem because of the cathode foloower circuit?
Apologies for the late response here. If you’re talking about the classic line Phono Circuit, it is important that the sections be matched on the 6or12sn7 follower tube. Though it’s less important than if they were in a voltage gain position. The same goes for the modern line circuit using the 6N6P.