Originally Posted by themicah
My hunch is that UAwatcher's assertion that CO EQMs are based on metal is correct. Every other CO or NW EQM situation seems to be based on the metal flown, not the code or ticket stock.
Let's throw ticket stock out for now. You can use aa.com and get various carriers issued on AA stock, so that's a moot point.
CO also knows (and now reports) the coding and fare basis. So while metal flown is part of it, each code has a fare basis that maps to another fare basis if it's a codeshare (e.g., NW K = CO L). CO knows both of these from your ticket.