Originally Posted by themicah
"Co-terminal" refers to routing rules, not fare eligibility rules.
If a fare is only available on JFK-IAH, it's not valid on EWR-IAH, so you best be hoping you've got a VERY understanding GA at EWR, or else you've just forfeited your $158 ticket.
Technically, it's not routing rules, rather fare calculation.
That said, you are one of the very few FTers who properly understands the intent behind co-terminals. ^