You can do that for paper tickets and even for tickets issued by other OW carriers (not AA) if Sabre has your itinerary info. Until the first schedule change and then the whole thing disappears with the admonition to phone AA for details of the schedule change. The sole advantage of e-tickets is not having to carry the paper tickets around; but lots of disadvantages (in the past 2 years I've had 2 e-tickets disappear from the system -- not on AA -- and the onus was on me to prove that the reservation existed ... one of those airlines is now on my blacklist). I'd love to have e-tickets work, but they are just not quite there yet for interlining.